ACUS48 KWNS 210906
SWOD48
SPC AC 210904

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0404 AM CDT Tue May 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
...Day 4/Fri - Mid MS Valley/Upper Great Lakes vicinity...

An upper shortwave trough over the northern Plains will pivot
northeast across the Upper Midwest on Friday. At the surface, low
pressure will develop northward across MN/WI and a trailing cold
front will push east, becoming positioned from WI to central OK/MO
by Saturday morning. Some severe potential is possible ahead of the
front from the Mid-MS Valley into the Great Lakes vicinity. However,
ongoing convection early Friday and large-scale ascent lifting
northeast of the region with time is resulting in uncertainty.
Severe probabilities will likely be needed in subsequent outlooks as
mesoscale details become better resolved, but confidence is too low
to delineate an unconditional 15 percent probability at this time.

...Day 5/Sat - Southern Plains to the Ozarks vicinity...

Low-amplitude west/southwest mid/upper flow is forecast across the
southern Plains to the Mid-South vicinity for much of the diurnal
period on Saturday. By 00z, forecast guidance suggests a shortwave
trough will eject from the southern Rockies into the southern
Plains, and eventually impinging on the Ozarks/Mid-South area by
Sunday morning. A very moist and unstable airmass is forecast over
the southern Plains vicinity ahead of this feature as a surface warm
front lifts northward through the day. Increasing ascent may not
arrive until after 00-03z, limiting convective initiation until the
nighttime hours. If storms can develop during the day across
portions of OK/TX, all hazards severe potential will exist.
Otherwise, thunderstorm potential may be more likely during the evening/overnight from north TX into southeast OK and AR as
large-scale ascent increases and a 65-75 kt 500 mb jet overspreads
the region. The north and west bounds of severe potential are a bit
uncertain, so this area may shift in subsequent outlooks.

...Day 6/Sun - Ozarks to the Lower OH and TN Valleys...

An upper shortwave trough will progress across the region on Sunday.
Forecast guidance depicts a 50-60 kt southwesterly 700 mb jet
overspreading the region during the day. Meanwhile, a surface low
will intensify over MO/IL, shifting northeast along the OH River
through the period. A very moist and unstable airmass is depicted
ahead of the low and attendant south/southeastward-progressing cold
front. Intense severe thunderstorms will likely accompany this
system. Consistency among deterministic guidance, favorable synoptic
pattern, as well as CSU/NSSL ML output, support introduction of 15
percent probabilities for Sunday.

...Days 7-8/Mon-Tue...

Spread among forecast guidance increases substantially by the end of
the forecast period. However, a pattern shift by Day 8/Tue appears
possible, with an amplified upper ridge potentially building over
the western half of the CONUS. Overall, predictability is too low to
delineate areas of severe potential across the eastern half of the
CONUS.

..Leitman.. 05/21/2024

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ACUS48 KWNS 220857
SWOD48
SPC AC 220856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Wed May 22 2024

Valid 251200Z - 301200Z

...DISCUSSION...
...Day 4/Sat - Central/Southern Plains to Mid-MS Valley...

An upper shortwave trough over AZ/NM is forecast to spread eastward
across the central/southern Plains to the Ozarks vicinity on
Saturday. As this occurs, southwesterly mid/upper flow will
increase. Height falls will induce surface cyclogenesis over western
KS and the OK/TX Panhandles during the daytime. In response, a warm
front will lift northward across central/eastern OK/KS and much of
the Mid-MS Valley. A surface dryline will extend south from the
surface low near the OK/TX border through evening. During the
nighttime hours, the surface low is forecast to develop
east/northeast into MO while a cold front overspreads parts of the central/southern Plains by Sunday morning.

A very moist and unstable airmass will develop over the region as
the warm front lifts north, allowing for strong destabilization. As
large-scale ascent and vertical shear increase during the
afternoon/evening, widespread thunderstorm development is expected.
Initial supercells appear possible near the dryline and surface low
over OK/KS. With time, an MCS may develop over part of the region
and spread east into AR/MO during the evening/overnight hours. All
severe hazards appear possible at this time, and higher
probabilities may be needed in subsequent outlooks as mesoscale
features become better resolved for highlighting any corridors of
greater severe risk within the broader region.

...Day 5/Sun - Ozarks to the Mid-MS/Lower OH/TN Valleys...

A synoptically concerning pattern is evident on Sunday across a
broad region of the central U.S. The upper trough from the Day 4/Sat
period will continue to shift east across the Midwest on Sunday.
This will allow strong mid/upper southwesterly flow to overspread
the region as a deepening surface low moves from MO toward Lake
Michigan. Strong to severe thunderstorms may be ongoing across parts
of MO/the Ozarks vicinity. Ahead of this activity, a rapidly
moistening boundary layer with upper 60s to low 70s F dewpoints is
expected to envelop much of the Mid-MS/OH/TN Valleys. Strong
destabilization and favorable vertical shear, along with an eastward-progressing cold front will support both supercell storms,
and possibly a developing QLCS, capable of all hazards. While
details regarding morning convection and storm mode remain somewhat
uncertain, higher-end severe potential appears possible with this
pattern across portions of the region from midday into the nighttime
hours.

...Days 6-8/Mon-Wed...

Spread among model guidance increases quite a bit by Monday. Some
severe potential is possible anywhere from the Southern states to
the Mid-Atlantic as the upper trough lifts east/northeast. However,
details regarding storm evolution on Day 5/Sun into early Monday,
along with differing evolution of the surface pattern by various
guidance results in low predictability.

By Tuesday and Wednesday, an upper ridge is expected to move from
the western U.S. into the Plains. This should mostly shut down
severe potential west of the MS River.

..Leitman.. 05/22/2024

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ACUS48 KWNS 240902
SWOD48
SPC AC 240900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Fri May 24 2024

Valid 271200Z - 011200Z

...DISCUSSION...
Medium-range models suggest that large-scale flow will become more
amplified across the northern mid-latitudes of the eastern Pacific
into North America late this weekend into at least the middle of
next week. This is forecast to include building mid-level ridging
inland of the Pacific coast, then across and east of the northern
Rockies by Wednesday, in advance of inland progressing large-scale
mid-level troughing. Downstream of this regime, there may be some
further consolidation of mid-level troughing east of the upper
Mississippi Valley through the northern and middle Atlantic
Seaboard, before one embedded perturbation possibly contributes to
cyclogenesis and an evolving cut-off low offshore of the northern
Mid Atlantic coast by late next week.

As a significant initial cyclone migrates northeast of the Upper
Great Lakes region on Memorial Day, there is some potential for
moistening, destabilization and increasing shear within its warm
sector to support at least some risk for severe thunderstorm
development across parts of the Northeast and Mid Atlantic.
However, the stabilizing influence of potentially extensive
convection and convective outflow upstream during preceding days is
a possible complicating factor, so less than 15 percent
probabilities will be maintained for now due to low predictability.

Thereafter, into the middle to latter portion of next week, strong
potential instability will become confined to the Gulf Coast
initially, then mainly across the plains immediately to the east of
the Rockies. While the risk for severe weather may not be
negligible, it currently appears that this may remain isolated to
widely scattered in nature.

..Kerr.. 05/24/2024

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ACUS48 KWNS 250844
SWOD48
SPC AC 250843

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0343 AM CDT Sat May 25 2024

Valid 281200Z - 021200Z

...DISCUSSION...
Downstream of initially modestly amplified flow across the northern mid-latitude Pacific into western North America, large-scale
mid-level troughing across and east of the Mississippi Valley may
continue to slowly shift eastward through the middle to latter
portion of next week. Ensemble output suggests that this regime
will remain progressive, but the evolution of the flow remains
uncertain, particularly across the Northwest and northern Rockies
into northern Great Plains.

In lower latitudes, guidance suggests that ridging may build along
an axis to the north-northeast of a subtropical high over central
Mexico, perhaps as far as the southeastern Great Plains and lower
Mississippi Valley by early next weekend. However, an initial
perturbation progressing around the crest of the ridging as early as
Tuesday could contribute strong thunderstorm development across
parts of eastern New Mexico into western Texas, where the boundary
layer may remain seasonably moist in the presence of steep lapse
rates.

Low-level moisture return northward into the lee of the northern
Rockies may remain marginal for severe thunderstorm development, as
forcing for ascent associated with troughing migrating inland of the
Pacific coast spreads across and east of the northern Rockies on
Wednesday.

..Kerr.. 05/25/2024

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ACUS48 KWNS 260851
SWOD48
SPC AC 260849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sun May 26 2024

Valid 291200Z - 031200Z

...DISCUSSION...
In general, medium-range models indicate that larger-scale mid/upper
troughing will slowly progress eastward across and offshore of the
Atlantic Seaboard through the middle to latter portion of the coming
work week. As this occurs, flow across the northern mid-latitudes
of the Pacific into North America may trend less amplified, while
flow across the southern mid- and subtropical latitudes trends a bit
more amplified. It appears that this may include modest mid-level
troughing approaching the California and Baja coast next weekend,
upstream of building large-scale ridging across the southern Rockies
through the middle and lower Mississippi Valley. Shorter wavelength developments are substantially more unclear throughout the period
due to sizable model spread.

Beneath this regime, moderate to strong potential instability,
associated with seasonably moist boundary-layer air beneath steep lower/mid-tropospheric lapse rates, may mostly remain confined to
the higher plains to the lee of the Front Range southward into the
Pecos Valley. As mid-level heights fall to the south of the
initially prominent trough slowly progressing to the east of the
northern Rockies late this week, it is possible that storms
developing in the late afternoons off the higher terrain could
evolve into clusters posing at least some severe weather threat
across the adjacent plains. However, due to generally low
predictability, severe weather probabilities are being maintained at
less than 15 percent.

..Kerr.. 05/26/2024

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ACUS48 KWNS 270843
SWOD48
SPC AC 270841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Mon May 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
On the leading edge of a slowly progressive regime emanating from
the northern mid-latitude Pacific, it appears that larger-scale
mid-level troughing will contribute to the suppression of amplified
downstream mid-level ridging across the Northwestern Ontario/Upper
Midwest vicinity late this week. Thereafter, potential flow
evolution across the eastern Pacific through North America next
weekend into early next week becomes highly uncertain due to
continuing sizable spread within/among the various medium-range
model output.

Undoubtedly, there will developing areas of sufficient
destabilization and shear to support at least some risk for
organized severe weather on a daily basis. However, there is little
indication at this time that this risk will exceed seasonal norms,
at least on a regional scale.

..Kerr.. 05/27/2024

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ACUS48 KWNS 270847
SWOD48
SPC AC 270846

Day 4-8 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
0346 AM CDT Mon May 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
On the leading edge of a slowly progressive regime emanating from
the northern mid-latitude Pacific, it appears that larger-scale
mid-level troughing will contribute to the suppression of amplified
downstream mid-level ridging across the Northwestern Ontario/Upper
Midwest vicinity late this week. Thereafter, potential flow
evolution across the eastern Pacific through North America next
weekend into early next week becomes highly uncertain due to
continuing sizable spread within/among the various medium-range
model output.

Undoubtedly, there will developing areas of sufficient
destabilization and shear to support at least some risk for
organized severe weather on a daily basis. However, there is little
indication at this time that this risk will exceed seasonal norms,
at least on a regional scale.

..Kerr.. 05/27/2024

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ACUS48 KWNS 280854
SWOD48
SPC AC 280853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0353 AM CDT Tue May 28 2024

Valid 311200Z - 051200Z

...DISCUSSION...
Medium-range guidance indicates that an initially prominent
mid-level ridge will become increasingly suppressed across the Great
Lakes region late this week into early next weekend. It appears
that flow will then trend more zonal along the interior
Canadian/U.S. border vicinity, but subsequent flow evolution remains
uncertain due to continuing notable spread within/among the various
model output. Broad mid-level ridging, within the stronger
westerlies emanating from the northern mid-latitude Pacific, is
generally forecast to build inland of the northern Pacific coast
through the western/central Canadian U.S. border area by the middle
of next week.

It is possible that this may be preceded by mid-level troughing
which may contribute to modest surface cyclogenesis, from the lee of
the northern Rockies through the middle Missouri Valley and northern
Great Plains Red River Valley by early next Monday, then across
northwestern Ontario Tuesday. It might not be out of the question
that increasing flow and shear, coupled with low-level moisture
return ahead of a sharpening dryline across the High Plains, could
contribute to an increase in severe weather potential late Sunday
afternoon. This could continue along a cold front overtaking the
dryline across the northern Great Plains into Upper Midwest, and
along the dryline across the central and southern High Plains, into Monday/Monday night.

..Kerr.. 05/28/2024

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ACUS48 KWNS 290859
SWOD48
SPC AC 290858

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CDT Wed May 29 2024

Valid 011200Z - 061200Z

...DISCUSSION...
The potential evolution of the mid/upper flow by this weekend into
next week remains rather uncertain, based on the continuing
substantial spread evident in the medium-range model output. It
currently appears most certain that the westerlies may undergo
substantial amplification across the mid-latitude Pacific into
western North America by the middle of next week, including broad
large-scale mid-level ridging building across the eastern Pacific
through much of the U.S. Intermountain West and Rockies. This may
be preceded by a period of more zonal flow near the Canadian/U.S.
border area, with a couple of embedded, progressive short wave
troughs.

Models suggest that these waves may be accompanied by surface
cyclogenesis to the lee of the Canadian/northern U.S. Rockies.
Initial cyclogenesis to the lee of the northern U.S. Rockies,
through the middle Missouri and northern Great Plains Red River
Valley, on Sunday may be modest. However, it appears possible that
increasing flow/vertical shear, and destabilization associated with
low-level moisture return, could become sufficient to support at
least some organized severe thunderstorm potential by Sunday
afternoon into Sunday night.

Guidance is suggestive that surface cyclogenesis with the trailing
wave next Tuesday may be stronger, but it remains unclear whether
this will be focused to the lee of the northern U.S. Rockies or to
the lee of the Canadian Rockies into the Canadian Prairies.

Due to the considerable uncertainties, severe probabilities are
being maintained at less than 15 percent through this period.
However, this could change in later outlook updates for this period, particularly in the Sunday through Tuesday time frame.

..Kerr.. 05/29/2024

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ACUS48 KWNS 300900
SWOD48
SPC AC 300859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Thu May 30 2024

Valid 021200Z - 071200Z

...DISCUSSION...
Medium-range models continue to indicate that flow across the
eastern mid-latitude Pacific into North America may undergo
substantive amplification during the middle to latter portion of
next week. This is forecast to include building larger-scale
ridging across much of the U.S. and Canadian Pacific coast through
the Canadian/northern U.S. Rockies.

Within an initially zonal regime preceding this evolution, guidance
continues to suggest that modest surface cyclogenesis may accompany
the eastward progression of a low-amplitude short wave trough, from
the lee of the northern Rockies through the middle Missouri and
northern Great Plains Red River Valley vicinity Sunday through
Sunday night. Moderately large CAPE may develop beneath a plume of
elevated mixed-layer air overspreading much of the Great Plains,
from the developing cyclone southward. Strongest forcing for ascent
and shear may focus the most substantive convective development from
near the surface low/dryline across central South Dakota by late
Sunday afternoon northeastward through central and southern
Minnesota by late Sunday afternoon and evening. This may include a
few supercells initially, before convection consolidates and grows
upscale into an organizing cluster. It currently appears that
sustained thunderstorm development may be much more isolated
southward along the dryline through the remainder of the Great
Plains.

A considerably stronger short wave trough may dig downstream of the
amplifying ridge by the early to middle portion of next week. This
may be accompanied by strong surface cyclogenesis, and perhaps the
evolution of a broad deep mid-level low centered over the Upper
Midwest/Great Lakes region by late next week. This might be
accompanied by a risk for strong to severe storms spreading from
portions of the northern and central Great Plains as far east as
portions of the Mid Atlantic and Northeast by late next week.
However, due to still large model spread, which increases by early
next week, severe probabilities are being maintained at less than 15
percent, but this could change in later outlooks for this period.

..Kerr.. 05/30/2024

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ACUS48 KWNS 310841
SWOD48
SPC AC 310840

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CDT Fri May 31 2024

Valid 031200Z - 081200Z

...DISCUSSION...
A shortwave trough will likely be moving through far northwestern
Ontario early Monday morning, with an attendant surface low tracking
just ahead of the shortwave. An associated cold front is forecast to
push eastward across the Upper Midwest and Upper Great Lakes. Modest
buoyancy and shear should limit the severe potential. Thunderstorms
are also possible farther south into the central Plains and Mid MS
Valley as low-level moisture advects northward, with the outflow
from Sunday's storms potentially returning north as a warm front.
Complexity to this convective evolution limits predictability at
this range.

Medium-range guidance is in relatively good agreement that a strong northern-stream shortwave trough will progress through the northern
Plains and Upper Midwest on D5/Tuesday, accompanied by cold
mid-level temperatures. Thunderstorms are possible along and ahead
of this system. Boundary-parallel flow suggested by the ECMWF would
favor a relatively slow storm motion and limited severe potential,
while the more progressive GFS has more westerly flow. Some severe
appears possible, but predictability is too low to introduce any
areas with this outlook.

Guidance then shows notable variability on how this wave
progress/evolves on D6/Wednesday through D8/Friday, with this
variability keeping predictability low.

..Mosier.. 05/31/2024

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ACUS48 KWNS 010829
SWOD48
SPC AC 010828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Sat Jun 01 2024

Valid 041200Z - 091200Z

...DISCUSSION...
Medium-range guidance has come into better agreement with the
evolution of the northern-stream shortwave trough expected to move
through the northern Plains and Upper Midwest on D4/Tuesday. Much of
guidance suite now suggests this wave will mature into a cyclone
over Manitoba on D5/Wednesday before then tracking southeastward
over Ontario and the Upper Great Lakes on D6/Thursday and D7/Friday.
Surface low will be stacked beneath the mid/upper level cyclone by D5/Wednesday, while an associated cold front moves
eastward/southeastward through the Upper Midwest and Mid MS Valley
on D4/Tuesday. This initial front will likely weaken on
D5/Wednesday, before another more substantial frontal push occurs on D6/Thursday, taking the front through much of the central Plains and
OH Valley.

Thunderstorms are possible along and ahead of this cold front,
beginning across the Upper Midwest on D4/Tuesday and continuing
across the central Plains on D5/Wednesday. Thunderstorms will remain
possible across the central Plains on D6/Thursday, with storms
possible across the middle/upper OH Valley as well.

Uncertainty regarding severe coverage precludes the need for an area
across the Upper Midwest on D4/Tuesday, while uncertainties
regarding frontal timing limit predictability on D5/Wednesday and
D6/Thursday.

The front is not expected to effect much of the southern Plains with
low-level moisture remaining over the region on D7/Friday and
D8/Saturday. This suggests some thunderstorms are possible but the
lack of any large, more synoptic scale features limits
predictability.

..Mosier.. 06/01/2024

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ACUS48 KWNS 020853
SWOD48
SPC AC 020852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Sun Jun 02 2024

Valid 051200Z - 101200Z

...DISCUSSION...
A mid-latitude cyclone is forecast to be over southern
Saskatchewan/Manitoba early D4/Wednesday before a shortwave trough
moves quickly southeastward through its base and the cyclone shifts
into the Upper Great Lakes region. Only slow eastward progression of
this cyclone from the Great Lakes into the Northeast is anticipated
on D5/Thursday and D6/Friday. A cold front associated with this
system will likely push eastward across the OH and TN Valleys on
D4/Wednesday, with another frontal surge possible across these areas
on D5/Thursday. Thunderstorms are possible ahead of these fronts,
although uncertainty regarding frontal timing as well as buoyancy
limits predictability.

Farther southwest, upper ridging is expected to build over the
western CONUS on D4/Wednesday through D6/Friday, with northwesterly
flow persisting across the Plains. Low-level moisture will be
limited across the central Plains on D4/Wednesday but some moisture
return is possible D5/Friday, which could promote thunderstorm
development. Uncertainty regarding this moisture return and
resultant buoyancy results in low forecast confidence.

Upper pattern predicted for the medium-range guidance diverges
notably after D5/Friday, although none of the guidance predicts any
substantial shortwave troughs. As a result, the severe potential
each day will likely depend strongly on mesoscale factors, which are
difficult to forecast at this range.

..Mosier.. 06/02/2024

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ACUS48 KWNS 030833
SWOD48
SPC AC 030832

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0332 AM CDT Mon Jun 03 2024

Valid 061200Z - 111200Z

...DISCUSSION...
Medium-range guidance continues to vary on the strength and
evolution of the mid-latitude cyclone forecast to be over the Upper
Great Lakes/southern Ontario vicinity early D4/Thursday. Even with
this variance, the overall pattern remains fairly similar with the
cyclone drifting gradually eastward/southeastward into the Northeast
from D4/Thursday through D6/Saturday. At the same time, upper
ridging is forecast to build from the southern Plains into the
Pacific Northwest/British Columbia. A belt of strong northwesterlies
is anticipated between these two features, from the Canadian
Prairies across the Upper Midwest and OH Valley and into the
Mid-Atlantic, through the weekend.

The greater low-level moisture and buoyancy will likely remain
confined to the southern Plains and Southeast on D4/Thursday and
D5/Friday, before some moisture advection takes it back into the
central Plains on D6/Saturday and D7/Sunday. No synoptic features
are forecast to interact with this moisture across the
southern/central Plains, but daily afternoon thunderstorm
development along the lee trough across central/southern High Plains
appears possible. However, predictability of coverage and severity
is low at this forecast range.

..Mosier.. 06/03/2024

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ACUS48 KWNS 040852
SWOD48
SPC AC 040850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Tue Jun 04 2024

Valid 071200Z - 121200Z

...DISCUSSION...
Medium-range guidance is in relatively good agreement that a mature
cyclone and associated troughing will cover much of the northeast
CONUS through the weekend. At the same time, ridging will build over
the western CONUS. This amplified trough/ridge pattern will likely
remain in place until at least D6/Sunday, but guidance has struggled
to converge on a solution from D6/Sunday through D8/Tuesday, with
the guidance showing notable run-to-run variability.

General expectation is for low-level moisture advection to result in
moderate to strong buoyancy over the central and southern High
Plains on D4/Friday and D5/Saturday. No synoptic features are
forecast to interact with this moisture, but daily afternoon
thunderstorm development along the lee trough across appears
possible. Forecast confidence decreases after D5/Saturday, with the
variability within the guidance resulting in limited predictability.
There is some chance the pattern remains fairly stagnant, with
additional days of afternoon southern/central High Plains storms
possible. However, the 00Z guidance suite has trended towards the
progression of a strong front across the central and eastern CONUS
on D6/Sunday and D7/Monday, with thunderstorms possible along the
front.

..Mosier.. 06/04/2024

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ACUS48 KWNS 050842
SWOD48
SPC AC 050840

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CDT Wed Jun 05 2024

Valid 081200Z - 131200Z

...DISCUSSION...
The large upper cyclone that is expected to persist across
southeastern Canada and the northeastern CONUS throughout the end of
the week will likely begin breaking down on D4/Saturday, when a
series of shortwave troughs begin progressing through its southern
periphery. The evolution of these shortwaves is expected to induce a
more progressive character to this cyclone while also amplifying the
troughing across the eastern CONUS on D5/Sunday. This upper
troughing is then forecast to shift eastward off the East Coast on
D6/Monday.

The evolution of this cyclone will encourage a southward push of
continental air across the central Plains and Mid MS/OH Valleys on
D4/Saturday, likely continuing southward across the southern Plains
and much of the Southeast on D5/Sunday. Upslope flow behind the
front may contribute to thunderstorms across the central High Plains
on D4/Saturday, with additional storms possible ahead of the front
over the Ozark Plateau vicinity. Uncertainty regarding frontal
timing as well as overall severe coverage limits predictability.
Thunderstorms are possible along the front across the southern
Plains and Southeast on D5/Sunday, but may trend towards a more
anafrontal character given the boundary-parallel orientation of the
deep-layer shear vector.

Guidance begins to diverge on D6/Monday, resulting significant
differences in forecast low-level moisture across the Plains and
Southeast States. These difference lower forecast confidence and
limit predictability.

..Mosier.. 06/05/2024

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ACUS48 KWNS 060902
SWOD48
SPC AC 060900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Thu Jun 06 2024

Valid 091200Z - 141200Z

...DISCUSSION...
Medium-range guidance has trended towards better agreement on the
upper pattern from D4/Sunday through D6/Tuesday. A series of
shortwave troughs are expected to progress through the base of a
parent upper trough over the northeast CONUS and Ontario/Quebec,
with this parent upper trough gradually shifting eastward. Upper
ridging is anticipated west of the this troughing, beginning over
the Plains and Canadian Prairies on D4/Sunday before gradually
shifting eastward. By early D6/Tuesday, general expectation is that
the upper trough will extend along the East Coast with ridging to
its west from the Mid MS Valley through the Upper Great Lakes into central/eastern Ontario and Quebec.

This evolution would place much of the stronger mid-level flow to
the north and east of the better low-level moisture, which is
expected to gradually shift south as a cold front moves through the
OH/TN Valleys and central Plains on D4/Sunday. The front will likely
continue into the Southeast on D5/Monday, while stalling across TX. Thunderstorms are possible along this front, but given the stronger
flow will be displaced north, any severe will likely be dictated by
less predictable mesoscale factors.

Moderate low-level moisture is expected to be in place over the High
Plains from D4/Sunday and D5/Monday. Thunderstorms are possible over
this region both of these days, but notable uncertainty regarding
storm coverage and intensity exists across the southern and central
High Plains. Greater coverage is expected across the northern High
Plains on D5/Monday when a northern-stream shortwave trough is
expected to progress through the region. Uncertain timing of this
wave and its associated cold front as well as uncertainty regarding
the moisture quality within the warm sector limit predictability.
Similar uncertainties exist on D6/Tuesday across the central Plains
and Mid/Lower MO Valley as the shortwave trough and associated front
continue eastward/southeastward.

Upper ridging will likely move into the Plains in the wake of this northern-stream shortwave trough, with some potential for troughing
to enter the Plains during the latter half of the week. Guidance
differs with the strength and timing of these features, limiting
forecast confidence.

..Mosier.. 06/06/2024

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ACUS48 KWNS 070851
SWOD48
SPC AC 070850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Fri Jun 07 2024

Valid 101200Z - 151200Z

...DISCUSSION...
...Monday/Day 4 to Wednesday/Day 6...
From Monday to Wednesday, model forecast spreads are unusually
large, suggesting that uncertainty is considerable. The ECMWF is
forecasting a shortwave trough to move through the northern High
Plains on Monday. If this trough materializes, then strong storms
would be possible in the Dakotas during the late afternoon and early
evening. This potential for strong storms appears to shift southward
into the southern Plains Tuesday, where the ECMWF has northwest flow
and moderate instability. On Wednesday, a severe threat could
develop in parts of the northern Plains once again, as low-level
moisture returns ahead of another shortwave trough. Due to the large
model spreads, confidence in any one scenario during the early to
mid week is quite low.

...Thursday/Day 7 and Friday/Day 8...
Large model spreads concerning potential outcomes continues on
Thursday and Friday. The ECMWF solution suggests that the greatest
potential for severe storms could be in the central Plains each day,
within the northern part of a moist and unstable airmass. The ECMWF
solution suggests that any potential for severe storms could remain
unfocused due to a lack of forcing within west-northwest mid-level
flow. Late in the Day 4 to 8 period, the large spread in model
solutions suggests that predictability remains unusually low.

..Broyles.. 06/07/2024

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ACUS48 KWNS 080855
SWOD48
SPC AC 080854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Sat Jun 08 2024

Valid 111200Z - 161200Z

...DISCUSSION...
...Tuesday/Day 4 to Thursday/Day 6...
Over the last few runs, medium-range model forecasts have become in
much better agreement during the mid-week. A shortwave trough is
forecast to move across the north-central U.S. on Tuesday, as
another trough moves eastward across the southern Plains. The models
suggest that there will be potential for strong thunderstorms
Tuesday afternoon in parts of Texas and Oklahoma. This potential for
strong thunderstorms moves eastward into the Ark-La-Tex on
Wednesday. A more appreciable severe threat could develop in parts
of the eastern Dakotas and upper Mississippi Valley on Wednesday, as
a mid-level jet translates eastward through the region. A 15 percent
contour has been added from western Minnesota and eastern North
Dakota southward into north-central Nebraska, where model consensus
suggests the environment will be most favorable for severe storms
during the late afternoon and early evening on Wednesday.

Uncertainty related to the most favorable area for severe weather
increases on Thursday. The ECMWF suggests that the greatest threat
will be in the upper Mississippi Valley. Other solutions suggest the
potential threat area could be further southwest into the lower to
mid Missouri Valley. The plan is to give the models a few more runs
before adding a 15 percent contour, so that confidence can be higher
concerning the severe threat positioning.

...Friday/Day 7 and Saturday/Day 8...
On Friday and Saturday, an upper-level ridge is forecast to move
eastward across the central and northern U.S. A moist and unstable
airmass may be located beneath the ridge across much of the Great
Plains and Missouri Valley. Thunderstorm development will be
possible each day, mostly concentrated near outflow boundaries and
in areas that heat up the most. The details concerning these factors
remains very uncertain at this extended range.

..Broyles.. 06/08/2024

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ACUS48 KWNS 090901
SWOD48
SPC AC 090900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Sun Jun 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
A low amplitude shortwave ridge is forecast to move across the
northern Plains on Wednesday, where a moist and unstable airmass
will likely be in place. Scattered thunderstorms will be possible
Wednesday afternoon across parts of this airmass from eastern South
Dakota and southwestern Minnesota southward into the mid Missouri
Valley. The medium-range models are in reasonable agreement, with
moderate deep-layer shear in place across much of the region. This
would be favorable for organized storms, with a severe threat
possible during the late afternoon and early evening.

On Thursday, a cold front is forecast to move southward into the mid
Missouri and mid Mississippi Valleys. A moist and unstable airmass
is forecast to the south of the front. Most models develop moderate
instability near and to the south of the front by afternoon, and
show potential for convective development. Model forecasts suggest
that moderate deep-layer shear will be in place across much of the
moist airmass, resulting a chance for organized thunderstorms from
late afternoon into the evening.

...Friday/Day 6 to Sunday/Day 8...
From Friday to Sunday, an upper-level ridge is forecast to move from
the north-central U.S. into the Great Lakes, as an upper-level
trough approaches the northern Plains. Ahead of the trough, isolated
to scattered strong to severe storms will be possible each day
across the north-central U.S. Based on the latest runs, the greatest
potential for severe would be on Sunday in the northern Plains, as
the upper-level trough approaches. However, model spread is large
during this three day time span, suggesting that severe threat
predictability is low.

..Broyles.. 06/09/2024

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ACUS48 KWNS 100858
SWOD48
SPC AC 100856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Mon Jun 10 2024

Valid 131200Z - 181200Z

...DISCUSSION...
...Thursday/Day 4 to Saturday/Day 6...
On Thursday, an upper-level trough is forecast to move into the
Great Lakes region, as a cold front advances southward across the
Central Plains and mid to upper Mississippi Valley. Moderate
instability is forecast south of the front by afternoon, where the
models suggest that scattered thunderstorm development will take
place. In addition, a mid-level jet is forecast to move eastward
across the north-central U.S. on Thursday. Moderate deep-layer shear
is forecast along the southern edge of this broad mid-level jet,
which should support a severe threat during the late afternoon and
early evening.

On Friday, an upper-level ridge is forecast to move across the
north-central U.S. Some models suggest that an axis of maximized
low-level moisture will setup beneath the ridge over the central
states. If this scenario pans out, then severe storms would be
possible Friday afternoon and evening across parts of the central
Plains. The presence of the ridge and the lack of large-scale ascent
casts doubt on any particular scenario.

On Saturday, a shortwave trough is forecast to move into the
southern High Plains, as the upper-level ridge moves into the upper
Mississippi Valley. In the wake of the ridge, a pocket of moderate
instability could be in place across the Dakotas and Minnesota, as
is suggested by the ECMWF. This area would be favored for severe
storm development. However, uncertainty is still substantial at this
range, especially due to significant spread among the model
solutions.

...Sunday/Day 7 and Monday/Day 8...
On Sunday and Monday, model forecasts suggest that a moist and
unstable airmass will be in place across much of the north-central
U.S., as multiple short troughs move northeastward through the
region. Scattered severe storms will be possible each day ahead of
these features in areas that destabilize the most, with the greatest
potential likely from Nebraska northward into the Dakotas. However,
model spread continues to be large late in the Day 4 to 8 period.
Once the model solutions become in better agreement, a 15 percent
contour may need to be added in parts of the north-central states
for either Sunday or Monday.

..Broyles.. 06/10/2024

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ACUS48 KWNS 110853
SWOD48
SPC AC 110852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Tue Jun 11 2024

Valid 141200Z - 191200Z

...DISCUSSION...
...Friday/Day 4 to Sunday/Day 6...
From Friday to Sunday, an upper-level ridge is forecast to move
eastward from the Great Plains to the northeast, as a shortwave
trough moves northeastward from the Four Corners to the upper
Mississippi Valley. A somewhat narrow corridor of instability,
oriented from southeast to northwest, is forecast ahead of the
trough on Friday and Saturday. As the trough moves out into the
central High Plains, isolated to scattered thunderstorms appear
likely to develop across parts the instability corridor, with the
greatest convective coverage likely in the evening and overnight
period when the airmass is less likely to be capped. A severe threat
could be associated with the stronger cells within the clusters that
form near areas of moderate to strong instability. The main
uncertainty involves the position of the instability axis relative
the approaching trough. Some models suggest that the two will be far
removed from each other, which introduces a lot of uncertainty
concerning any potential scenario.

On Sunday, the shortwave trough is forecast to move into the upper
Mississippi Valley, and out-run the stronger instability located in
the mid Missouri Valley. Strong to potentially severe storms may
still develop in association with the trough, but the forecast
position of the warm sector relative to the trough introduces
uncertainty into the forecast.

...Monday/Day 7 and Tuesday/Day 8...
On Monday, an upper-level trough is forecast to move into the
western U.S., as southwest mid-level flow remains over much of the
central U.S. It appears that a moist and unstable airmass will be
located from the central Plains into the upper Mississippi Valley,
where isolated to scattered strong to severe storms will be possible
each day. However, model spread is large concerning the timing of
shortwave features and the positioning of instability. For this
reason, uncertainty is considerable for Monday and Tuesday.

..Broyles.. 06/11/2024

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ACUS48 KWNS 120901
SWOD48
SPC AC 120900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Wed Jun 12 2024

Valid 151200Z - 201200Z

...DISCUSSION...
...Saturday/Day 4 to Saturday/Day 5...
On Saturday, an upper-level trough is forecast to move northeastward
across the southern and central High Plains. An axis of instability
is forecast to be further to the northwest across the western
Dakotas. As a mid-level jet passes northeastward across the northern
Rockies, large-scale ascent and deep-layer shear should be strong
enough for an isolated severe thunderstorms in parts of the northern
High Plains. Large hail and severe wind gusts will be possible, but
uncertainty exists concerning the spatial distribution of the
threat.

The trough in the central Plains is forecast to move into the upper
Mississippi Valley on Sunday, with a large pocket of instability
located in its wake across the central Plains. Although large-scale
ascent within this unstable airmass is expected to be weak, isolated
severe storms could develop in the late afternoon and early evening.


Further to the northwest, model forecasts show potential for storm
development in parts of the northern High Plains Sunday evening. If
this were to occur, MCS development, and an isolated severe threat,
could occur across parts of the northern Plains Sunday night.

...Monday/Day 6 to Wednesday/Day 8...
On Monday, a mid-level jet is forecast to move northeastward into
the northern Plains, as a moist and unstable airmass remains in
place across the Upper Midwest. Severe thunderstorms may develop
across parts of the region during the afternoon and evening, in
association with any shortwave trough that can translate through the
flow. The models suggest there is enough potential on Monday for a
more widespread severe threat, to add a 15 percent contour in parts
of the eastern Dakotas and Minnesota.

On Tuesday, an upper-level trough is forecast to move across the
northern Plains. Isolated strong to severe thunderstorms would be
possible ahead of the trough in parts of the upper Mississippi
Valley. As the trough moves through southeastern Canada on
Wednesday, severe storms would be possible in parts of the
Northeast. However, uncertainty is considerable at this range in the
forecast period.

..Broyles.. 06/12/2024

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ACUS48 KWNS 130716
SWOD48
SPC AC 130714

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0214 AM CDT Thu Jun 13 2024

Valid 161200Z - 211200Z

...DISCUSSION...
...Day 5/Monday -- Eastern Dakotas/Minnesota...

A southwesterly midlevel jet is forecast to overspread a seasonally moist/unstable environment on Monday. Large-scale ascent will remain
somewhat nebulous as the more apparent synoptic upper trough remains
over the northern Rockies. However, forecast guidance suggests a
lead shortwave impulse may migrate through southwesterly mid/upper
flow. Favorable vertical shear will support organized severe storms,
though coverage and convective evolution remains uncertain.

...Days 6-8/Tue-Thu...

Beyond Day 5/Monday, forecast guidance generally shows an overall
slower trend with eastward progress of a western upper trough.
Severe potential may increase across portions of the
northern/central Plains around Day 6/Tue or Day 7/Wed if the trough
ejects east/northeast. If this occurs, enhanced deep-layer
southwesterly flow would overspread a seasonally moist and unstable
environment ahead of a southeastward-advancing cold front. This
overall pattern would support some severe potential somewhere from
the northern into central Plains. The GFS suite of guidance is more
progressive and favors this scenario. However, the ECMWF maintains a
stronger eastern upper ridge with little eastward progression of the
western upper trough through mid-week. Nevertheless, a broad area
of enhanced deep-layer southwesterly flow will impinge on the
northern Plains vicinity, and some severe potential seems probable,
but location and timing is too uncertain to include probabilities.

..Leitman.. 06/13/2024

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ACUS48 KWNS 140824
SWOD48
SPC AC 140823

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0323 AM CDT Fri Jun 14 2024

Valid 171200Z - 221200Z

...DISCUSSION...
Models indicate a strong upper ridge over much of the East and mean
troughing over the western states for much of the period. While
moderate southwest flow aloft will persist over parts of the
northern Rockies and Plains, timing of the emerging features is
uncertain. At this time, it appears a shortwave trough may move into
the northern Plains on Tue/D5 as opposed to Mon/D4. Further,
significant areas of early day convection appear possible on Mon/D4
and Tue/D5, which reduces predictability further. However, air mass
recovery is likely over parts of the northern Plains/Upper MS Valley
on Mon/D4, with clusters of storms producing areas of damaging wind
and locally severe hail. As such, will maintain the ongoing 15% area
for Mon/D4. Additional areas of severe hail/wind will be possible
on Tuesday/D5, but predictability is low given the tendency for the
eastern ridge to hold.

..Jewell.. 06/14/2024

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ACUS48 KWNS 150857
SWOD48
SPC AC 150856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Sat Jun 15 2024

Valid 181200Z - 231200Z

...DISCUSSION...
For the period, a strong upper ridge is forecast to remain over the
East. An upper trough will move into the northern Plains on
Tuesday/D4 and Wednesday/D5, with most of the energy moving into
eastern Canada thereafter. To the west, only a weak upper trough is
forecast.

Thunderstorms will be possible from MN southwestward into the
central Plains on Tuesday/D4 along a cold front, and some severe
threat appears likely as the stronger midlevel southwesterlies
extend from MN into NE. Instability will begin to be limited by
warming temperatures aloft, but ample low-level moisture will remain
ahead off the cold front with mid to upper 60s F dewpoints common. Front-parallel flow and a progressive cold front will likely yield
areas of damaging wind potential, and a 15% area has been introduced
near the surface low over northern Minnesota.

Severe storms chances are forecast to lessen by Wednesday/D5 over
the Plains/Upper MS Valley as the stronger winds aloft shift out of
the area.

..Jewell.. 06/15/2024

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ACUS48 KWNS 160843
SWOD48
SPC AC 160841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Sun Jun 16 2024

Valid 191200Z - 241200Z

...DISCUSSION...
From Wednesday/D4 into Thursday/D5, an upper trough will move from
Manitoba toward Hudson Bay, with the base of the trough shifting out
of ND/MN. This wave will continue east/northeast into Quebec,
flattening the ridge over the northeastern states. Meanwhile, upper
troughing will exist over the Great Basin, with moderately cool
temperatures aloft. Scattered storms will be likely along the
trailing front from the central Plains into the upper Great Lakes,
with perhaps a marginal severe risk given weaker shear and
instability.

Models indicate this western trough may emerge into the northern
Plains Friday/D6 into Saturday/D7, providing perhaps 40 kt midlevel
westerly winds and modest cooling aloft. Such a system may support
areas of strong storms, but overall the threat does not appear
particularly high. However, pockets of stronger instability could
support scattered hail and wind.

..Jewell.. 06/16/2024

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ACUS48 KWNS 170900
SWOD48
SPC AC 170859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Mon Jun 17 2024

Valid 201200Z - 251200Z

...DISCUSSION...
Models are in good agreement showing minimal severe potential for
much of the period, with generally weak winds aloft across the CONUS
and an upper high over much of the East. There is some indication
that the northern-stream may become more active along the US/CA
border starting around Saturday/D6 or Sunday/D7, mainly from the
upper MS Valley across the Great Lakes. Instability would appear to
be weak to moderate, and at least a low threat of severe storms may
materialize from MN to MI. Should such a trough occur, a strong
storm threat could extend into the Northeast as well toward
Monday/D8. Otherwise, the weak winds aloft and generally high
heights should preclude much potential across the remainder of the
CONUS through the period.

..Jewell.. 06/17/2024

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ACUS48 KWNS 180733
SWOD48
SPC AC 180732

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0232 AM CDT Tue Jun 18 2024

Valid 211200Z - 261200Z

...DISCUSSION...
For Friday/D4 into Saturday/D5, models indicate potential for a
shortwave trough to move out of the western US and across the
northern Plains and upper MS Valley. However, predictability is
already low by this time, with little run-to-run consistency
regarding the strength of the trough. While thunderstorms appear
likely across the region during the time frame, the degree of severe
potential remains in question. The ECMWF appears to be trending
toward a stronger trough solution in recent runs.

If this trough develops, it is expected to continue across the Great
Lakes and Northeast for the Sunday/D6 to Monday/D7 period.
Increasing flow fields with such a trough would likely result in
increased severe potential, conditional on sufficient instability
developing. Details aside, the primary message for the D4-8 period
is a breakdown of the upper ridge in the East, with a somewhat
progressive northern-stream storm track along the northern border
states, with at least low-end severe areas likely in later outlooks
as predictability increases.

..Jewell.. 06/18/2024

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ACUS48 KWNS 190820
SWOD48
SPC AC 190818

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0318 AM CDT Wed Jun 19 2024

Valid 221200Z - 271200Z

...DISCUSSION...
Models indicate a shortwave trough and possible lead wave over the
northern Plains on Saturday/D4 will move east/southeast toward the
Great Lakes and then into the Northeast through Sunday/D5. There is
quite a bit of variability with this setup, and as a result
predictability is low. However, at least a low-end risk of severe
storms may occur over the upper MS Valley/Upper Great Lakes on
Saturday/D4. Instability looks to get weaker as the trough shifts
into the Northeast on Sunday/D5, but any of the stronger trough
solutions could pose at least a marginal risk for severe weather at
that time.

From Monday/D6 and beyond, it appears the stronger flow aloft will
be relegated to the US/CN border, with generally low severe
potential across the CONUS.

..Jewell.. 06/19/2024

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ACUS48 KWNS 200746
SWOD48
SPC AC 200744

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 AM CDT Thu Jun 20 2024

Valid 231200Z - 281200Z

...DISCUSSION...
On Monday/D5, and upper trough is forecast to move across the Great
Lakes and into the Northeast. The primary surface low will be well
to the north in Quebec, but a cold front will extend south and
likely interaction with a moist and marginally unstable air mass
with at least 1000 J/kg MUCAPE. This may yield areas of strong
storms over the region, and the trough progression will need to be
monitored in upcoming outlooks.

For Tuesday/D6 through Thursday/D8 period, a strong upper ridge is
forecast over the Four Corners states, with strong northwest flow
possibly developing from the northern Plains, upper MS Valley and
Great Lakes. This type of setup could result in a severe MCS pattern
over parts of the northern Plains to Midwest with damaging wind
potential, possibly beginning as early as late Monday/D5 over the
northern Plains and upper MS Valley. Predictability of the potential
severe corridors is low at this time, but severe areas could be
introduced in later outlooks.

..Jewell.. 06/20/2024

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ACUS48 KWNS 210848
SWOD48
SPC AC 210846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Fri Jun 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
...D4/Monday: Northern Plains into the upper MS Valley/Great
Lakes...
A mid/upper-level shortwave trough and deepening surface low are
forecast to move across parts of SK/MB on Monday. A surface trough
will extend southward from the low into the northern Great Plains,
with secondary surface low development possible across the Dakotas.
A warm front will move northeastward somewhere from the eastern
Dakotas into the upper MS Valley. Strong buoyancy is forecast to
develop near and to the south/west of the warm front, with favorable
deep-layer shear providing a conditionally favorable environment for
severe thunderstorms.

While some severe potential appears likely to evolve somewhere from
the northern Plains into the upper MS Valley and/or upper Great
Lakes, guidance varies regarding the position of the warm front, and
also the southern extent of height falls and large-scale ascent
attendant to the SK/MB shortwave trough. Much of the warm sector
will likely remain capped, but severe storm development will be
possible in closer proximity to the warm front and secondary surface
low, which could potentially grow upscale and move southeastward
along the instability gradient. Severe probabilities will likely be
needed once confidence increases regarding the placement of the
primary surface features.

...D5/Tuesday: Upper Midwest into the central/southern Plains...
The shortwave trough that moves across parts of SK/MB on Monday is
generally forecast to move east-southeastward on Tuesday across
parts of ON and the upper Great Lakes. Model spread regarding the
timing and track of this shortwave continues to increase at this
time range, and the potential for MCS development on D4/Monday
further reduces predictability regarding the severe threat on
Tuesday. However, some severe-thunderstorm potential may evolve
along a southeastward moving cold front from the Great Lakes/upper
Midwest into parts of the central/southern Great Plains.

...D6/Wednesday - D8/Friday...
Some threat for strong to severe thunderstorms could continue to
accompany a southeastward-moving cold front on D6/Wednesday from the
southern Plains into the Ohio Valley and Northeast, though
predictability remains low regarding the details at this time range.

By D7/Thursday into D8/Friday, extended-range guidance generally
suggests the potential for a mid/upper-level shortwave trough to
move across the northern Rockies toward the northern High Plains.
However, model spread remains rather high regarding the evolution of
moisture return and any increasing severe potential in association
with this system.

..Dean.. 06/21/2024

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ACUS48 KWNS 220813
SWOD48
SPC AC 220812

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0312 AM CDT Sat Jun 22 2024

Valid 251200Z - 301200Z

...DISCUSSION...
...D4/Tuesday: Central Great Plains into the upper Midwest...
Some severe-thunderstorm potential may evolve from the central Great
Plains into the upper Midwest on Tuesday, along/ahead of a
southward-moving cold front. Uncertainty remains regarding storm
evolution leading into this period from D3/Monday, with some
potential for the cold front to become increasingly displaced from
stronger flow aloft. However, moderate to strong buoyancy and at
least modest deep-layer shear could support strong to severe storms
Tuesday afternoon/evening.

...D5/Wednesday: Central/southern Great Plains into the OH Valley
and Northeast...
Some threat for strong to severe storms will again be possible near
the cold front Wednesday afternoon and evening, which is generally
forecast to be draped from the south-central Great Plains
northeastward across the OH Valley into parts of the Northeast.
There is some potential for a stronger mid/upper-level shortwave
trough to interact with the front across the Northeast, though
instability may remain somewhat limited. Farther southwest into the
Plains, pre-frontal instability will be greater, but deep-layer
shear is expected to remain rather weak.

...D6/Thursday - D8/Saturday...
Extended-range guidance generally supports potential for a
mid/upper-level shortwave trough to amplify and move across the
northern CONUS by the end of next week, though there is considerable
spread regarding the timing of any such shortwave. While
predictability is too low to introduce probabilities at this time,
there is potential for an organized severe-thunderstorm threat to
evolve somewhere from the northern Plains into the Great Lakes and
Northeast, during the Thursday to Saturday time frame.

..Dean.. 06/22/2024

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ACUS48 KWNS 230816
SWOD48
SPC AC 230815

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0315 AM CDT Sun Jun 23 2024

Valid 261200Z - 011200Z

...DISCUSSION...
...D4/Wednesday...
Some threat for strong to severe storms may evolve from the OH
Valley into the Ozarks vicinity, in association with a
southeastward-moving cold front. However, the uncertain effects of
antecedent convection and a tendency for the front to become
displaced from stronger flow aloft render both the placement and
magnitude of the severe threat uncertain. Some severe threat could
also develop across parts of the Northeast, with a mid/upper-level
shortwave trough expected to move through the region in conjunction
with the cold front, but uncertainty remains regarding the potential
for moisture return and destabilization in advance of the front.

...D5/Thursday to D7/Saturday...
Extended-range guidance generally agrees that a rather amplified mid/upper-level shortwave trough will move across the northern
CONUS, sometime during the Thursday to Saturday time frame. Some
important differences remain, however, regarding the timing of the
shortwave and the evolution of the surface pattern and moisture
return. In general, some organized severe-thunderstorm potential may
spread across parts of the northern/central Plains, upper
Midwest/Great Lakes, and potentially the Northeast late this week
into the weekend.

..Dean.. 06/23/2024

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ACUS48 KWNS 240854
SWOD48
SPC AC 240852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Mon Jun 24 2024

Valid 271200Z - 021200Z

...DISCUSSION...
...D4/Thursday: Northern High Plains...
A rather amplified mid/upper-level shortwave trough is forecast to
move from the Northwest toward the northern Rockies on Thursday,
reaching the northern High Plains later Thursday night. A surface
low is forecast to deepen across eastern MT during the day, and then
move eastward across the Dakotas Thursday night.

Some uncertainty remains regarding the magnitude and placement of
organized severe-thunderstorm potential, due to the relatively late
shortwave arrival and a tendency for stronger mid/upper-level flow
to be displaced from the warm sector. However, modest low-level
moisture return will support potential for moderate destabilization,
in conjunction with some increase in deep-layer flow/shear. Some
potential for strong to severe storms is evident from eastern MT
into the western and possibly central Dakotas, and probabilities
will likely be needed in subsequent outlooks.

...D5/Friday: Northern/central Plains into the upper Midwest...
The shortwave trough and related surface low that affect the
northern High Plains on Thursday will move eastward on Friday, as a
trailing cold front moves across parts of the central Plains. A warm
front will move northward in advance of the surface low across parts
of MN/WI. Details regarding the northward extent of stronger
destabilization remain uncertain, with some potential for rather
extensive early-day convection within a warm-advection regime.
However, an organized severe-thunderstorm threat could eventually
evolve in conjunction with the surface low and warm front across
MN/WI, and also potentially along the cold front into parts of Iowa
and the central Plains.

...D6/Saturday - D8/Monday...
Predictability begins to wane by D6/Saturday regarding evolution of
the upper pattern and surface features across the CONUS. The cold
front that moves across parts of the Great Plains and Midwest on
Friday is generally forecast to move across parts of the Great Lakes
and Northeast on Saturday. Guidance varies regarding the extent of
prefrontal destabilization and strength of deep-layer flow, but
strong to potentially severe storms could develop along the front by
Saturday afternoon/evening.

Another mid/upper-level trough may move from the Northwest across
the northern Rockies and High Plains Sunday into Monday, though
considerable uncertainty remains regarding the amplitude/timing of
this trough and any related severe potential into early next week.

..Dean.. 06/24/2024

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ACUS48 KWNS 260840
SWOD48
SPC AC 260838

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0338 AM CDT Wed Jun 26 2024

Valid 291200Z - 041200Z

...DISCUSSION...
...D4/Saturday: Central/southern Plains into the Midwest/OH
Valley/Northeast...
A mid/upper-level trough is forecast to move from the upper Great
Lakes across parts of Ontario and Quebec on D4/Saturday, in
conjunction with a surface cyclone. A belt of relatively strong
mid/upper-level flow will move eastward along the southern periphery
of this trough. The extent to which the stronger flow overlaps the
warm sector of the cyclone is somewhat uncertain, but a corridor of
organized severe-thunderstorm potential could evolve across parts of
the Midwest/OH Valley into parts of the Northeast.

Farther southwest, a cold front moving across the Ozarks vicinity
and central/southern Plains will tend to be displaced from stronger
flow aloft. However, potentially strong instability could support
some severe threat in association with the front from parts of
southern KS and OK into northern AR and southern MO.

...D5/Sunday: Mid Atlantic into the Northeast...
Timing of the cold front that moves across parts of the Great Lakes
on Saturday becomes increasingly uncertain by Sunday. However, a
slower frontal progression would allow development of strong to
potentially severe thunderstorms from parts of the Mid Atlantic into
the Northeast.

...D5/Sunday: Central/northern High Plains...
A mid/upper-level trough is generally forecast to move from the
Northwest across the northern Rockies on Sunday. Some low-level
moisture return is expected to the east of a developing surface low
across WY/MT. Depending on the timing of the trough and magnitude of
moisture return, strong to severe thunderstorms will be possible
across parts of the northern/central High Plains Sunday
afternoon/evening.

...D6/Monday into D7/Tuesday: Parts of the central/northern Great
Plains into the Midwest...
The mid/upper-level trough that moves across the northern Rockies on
Sunday is forecast to continue eastward into the northern/central
Great Plains on Monday, as a surface low moves northeastward across
the Dakotas in conjunction with a warm front. The corridor of
favorable instability may be relatively confined due to the
influence of a surface ridge covering much of the eastern CONUS, but
some severe-thunderstorm potential could evolve from parts of the
Dakotas southward into KS/NE, and potentially farther east into
MN/IA/MO.

Depending on the extent of moisture return and destabilization, some
severe potential could spread into a larger part of the Midwest on
D7/Tuesday, as the mid/upper-level trough continues eastward.

..Dean.. 06/26/2024

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ACUS48 KWNS 270902
SWOD48
SPC AC 270900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Thu Jun 27 2024

Valid 301200Z - 051200Z

...DISCUSSION...
...D4/Sunday: Eastern MT into western ND...
A mid/upper-level trough will move eastward from the Northwest
toward the northern Rockies on Sunday, with some influence of this
trough reaching the northern High Plains by late afternoon into
early evening. Low-level moisture return north of a surface low
across WY will support moderate destabilization across parts of
eastern MT. Scattered storm development will be possible by early
evening as the mid/upper trough approaches. Increasing midlevel flow
will support initial supercell development, with a threat of large
hail. A strengthening nocturnal low-level jet will aid in potential
MCS development, which may spread some severe-wind potential into at
least western ND Sunday night.

...D4/Sunday: Southern New England into the Mid Atlantic...
Depending on the influence of early-day convection and timing of a
cold front, some modest destabilization may occur from southern New
England into the Mid Atlantic Sunday afternoon. Deep-layer shear
would support some storm organization, and strong to locally severe
storms will be possible.

...D5/Monday: Central/northern Great Plains...
The mid/upper-level trough that moves across the northern Rockies on
Sunday is forecast to emerge over the northern/central Great Plains
on Sunday. Moderate to locally strong destabilization will be
possible near and west of a warm front that is forecast to lift
northeastward through the day. Deep-layer shear will increase as
midlevel height falls overspread the warm sector, and scattered
strong to severe storms may develop in the vicinity of a trailing
surface trough/cold front. Supercells will be possible with initial development, with a potential tendency for some clustering/upscale
growth with time.

A 15% probability area has been included across parts of SD/NE,
where confidence is currently greatest in severe-storm development.
Some severe threat could also evolve across parts of ND, but there
is greater uncertainty with northward extent due to the potential
for an early-day MCS. Farther east, guidance varies regarding the
potential for destabilization into parts of MN/IA.

...D6/Tuesday: East-central Plains into the upper Midwest...
Some severe threat could spread eastward into parts of the
east-central Plains and Midwest on Tuesday, in conjunction with the eastward-moving mid/upper-level trough and attendant cold front.
However, predictability is currently too low to include
probabilities, due to uncertainty regarding trough evolution and the
influence of antecedent convection.

..Dean.. 06/27/2024

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ACUS48 KWNS 280902
SWOD48
SPC AC 280900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Fri Jun 28 2024

Valid 011200Z - 061200Z

...DISCUSSION...
...D4/Monday: Central/northern Great Plains...
A mid/upper-level trough with multiple embedded vorticity maxima is
forecast to move eastward across the northern/central Great Plains
on Monday. A surface low is forecast to deepen over the Dakotas,
along a surface trough. A warm front will lift northward across the central/northern Plains through the day, with very rich low-level
moisture in place along/west of the warm front, and east of a weak
cold front that will move into the western Dakotas.

Some uncertainty remains regarding the potential for morning
convection to limit destabilization with eastward and northward
extent. However, moderate to strong buoyancy is forecast to develop
from parts of the Dakotas into Nebraska, with increasing low-level
and deep-layer shear supporting the potential for organized
convection. Scattered thunderstorm development will be possible in
the vicinity of the various surface boundaries across the region as
midlevel height falls overspread the region. Initial storms may
evolve into supercells, with a threat for all severe hazards. Some
upscale growth is possible into the evening as storms spread
eastward, with a continued severe risk potentially reaching parts of
western MN/IA by Monday night.

...D5/Tuesday: East-central Plains into the Upper Midwest...
Some severe threat could develop on Tuesday from parts of the
east-central Plains into the upper Midwest, in conjunction with the eastward-moving mid/upper-level trough and attendant cold front.
Deep-layer shear will remain favorable for organized convection,
with potential for strong destabilization across areas where
stronger diurnal heating occurs.

However, uncertainty remains rather high regarding the favored
corridor for severe thunderstorm development, given model
differences in handling of the upper trough, and the potential for
extensive antecedent convection. Severe probabilities will likely be
needed at some point for parts of the region in subsequent outlooks.

...D6/Wednesday - D8/Friday...
Predictability begins to wane regarding the evolution of the surface
and upper patterns by mid to late next week. Some severe threat may
evolve across the Midwest on Wednesday in association with a cold
front. A developing northwesterly flow regime could result in
increasing severe potential across the Great Plains by Thursday into
Friday, but uncertainty remains high regarding the details.

..Dean.. 06/28/2024

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ACUS48 KWNS 290858
SWOD48
SPC AC 290856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Sat Jun 29 2024

Valid 021200Z - 071200Z

...DISCUSSION...
...Day 4/Tuesday for Corn Belt/Upper Midwest...
An amplifying shortwave trough and eastward-shifting strong early
summertime speed max will continue to influence the region on
Tuesday. Lingering convection/outflow from Monday night will likely
be a factor as far as spatial details, but it currently appears that
a very moist/unstable warm sector will focus across Iowa into
Tuesday afternoon and evening, ahead of a southeastward-moving cold
front. Seasonally strong winds would likely support potentially
intense and sustained storms including supercells. Have introduced
15 percent severe probabilities for this scenario, although spatial
adjustments and refinements will be needed in future outlooks.

...Day 5/Wednesday...
At least some severe-weather potential will likely exist across
parts of the Midwest and Ohio Valley within the moist/unstable
environment ahead of the advancing cold front. However, deep-layer
shear atop the warm sector will likely be weaker as compared to
prior days. Additional severe storms may occur near/north of the
synoptic front across the central Plains. Limited predictability and risk-magnitude uncertainties currently precludes 15+ percent
severe-weather probability delineations for these scenarios.

...Days 6-8 Thursday-Saturday...
Predictability wanes into this time frame, although corridors of at
least some severe storms can be expected daily, generally spanning
the northern/central Plains to the Ohio Valley and potentially parts
of the East.

..Guyer.. 06/29/2024

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ACUS48 KWNS 300900
SWOD48
SPC AC 300859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Sun Jun 30 2024

Valid 031200Z - 081200Z

...DISCUSSION...
...Day 4/Wednesday...
At least some severe-weather potential will likely exist across
parts of the Midwest and south-central Plains within the
moist/unstable environment ahead of the advancing cold front and
reinforcing outflows. This severe potential could include a corridor
from Ohio/Indiana/Illinois southwestward across the Ozarks into
Kansas and northern Oklahoma. Deep-layer shear atop the warm sector
will likely be weaker as compared to prior days. Additional severe
storms may occur near/north of the synoptic front across the
north-central High Plains. Risk-magnitude uncertainties still
preclude 15+ percent severe-weather probability delineations for
these scenarios.

...Day 5/Thursday Midwest including Iowa/Missouri...
Guidance is in relatively good agreement that a shortwave trough,
and strong jet in its base, will overspread the north-central Great
Plains toward the Upper Midwest on Thursday. Ahead of this
mid/upper-level trough, very favorable ingredients, including ample
instability and rather strong deep-layer shear for the season, may
set up across the southern half of Iowa, northern half of Missouri,
and possibly nearby parts of southeast Nebraska/northeast Kansas and
western Illinois. However, the potential impacts of convection
Wednesday night remain a key uncertainty regionally, and will thus
defer to future outlooks for an introduction of 15+ percent severe probabilities.

...Days 6-8 Friday-Sunday...
Predictability diminishes into this time frame, although corridors
of at least some severe storms can be expected daily, generally
spanning the northern/central Plains to the Ohio Valley and
potentially parts of the East. For instance, on Day 6/Friday,
related to the east-northeastward progression of the upper trough,
an area of interest includes parts of the Ohio Valley toward the
Lake Erie vicinity.

..Guyer.. 06/30/2024

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ACUS48 KWNS 010907
SWOD48
SPC AC 010906

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0406 AM CDT Mon Jul 01 2024

Valid 041200Z - 091200Z

...DISCUSSION...
...Day 4/Thursday Central Plains and Lower/Middle MO Valley...
Guidance remains in relatively good agreement that a shortwave
trough, and strong jet in its base, will overspread the
north-central Great Plains toward the Upper Midwest Thursday. Ahead
of this mid/upper-level trough, very favorable ingredients,
including ample instability and rather strong deep-layer shear for
the season, should set up across Missouri, southern Iowa, and
southeast Nebraska/northeast Kansas. The potential impacts of
convection lingering from Wednesday night remain a key uncertainty
regionally regarding the north-northeast extent of the more
appreciable severe risk, but the aforementioned areas seemingly have
the highest severe potential.

...Day 5/Friday Midwest...
While modest predictability precludes a 15+ percent severe risk at
this juncture, it seems probable that severe potential will be
focused within a moist and unstable air mass near/ahead of an east/southeastward-moving cold front. This may be most focused
across the Ohio Valley and other parts of the Midwest/Lake Erie
vicinity, with damaging winds expected to be the most common severe
hazard.

...Days 6-8 Saturday-Monday...
Predictability diminishes into this time frame, although corridors
of at least some severe storms can be expected daily, generally
spanning the northern/central Plains to the Ohio Valley, and
probably parts of the Mid-Atlantic/Northeast States on Day
6/Saturday.

..Guyer.. 07/01/2024

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ACUS48 KWNS 020903
SWOD48
SPC AC 020902

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0402 AM CDT Tue Jul 02 2024

Valid 051200Z - 101200Z

...DISCUSSION...
...Day 4/Friday Midwest and Ohio Valley...
While modest predictability continues to preclude a 15+ percent
severe risk at this juncture, it seems probable that severe
thunderstorm potential will be focused within a moist and unstable
air mass near and ahead of an east/southeastward-moving cold front.
This is most probable across the Ohio Valley and other parts of the Midwest/Lake Erie vicinity including states such as Kentucky and
Ohio. Damaging winds are expected to be the most common severe
hazard.

...Day 5/Saturday...
Severe-thunderstorm potential should spread eastward into the Northeast/Mid-Atlantic States in relation to the low-amplitude
shortwave trough and eastward-moving cold front. Other at least
isolated severe storms may occur across the northern Plains/Upper
Midwest, generally related to an amplifying shortwave trough and
weak front. Risk magnitude uncertainties preclude 15+ percent severe
risk areas.

...Days 6-8 Sunday-Tuesday...
Daily severe-weather potential can be expected, although specific predictability is limited into this time frame, as is typical for
this season. Early estimates are that severe-storm potential could
increase across the south-central Plains to Upper Midwest on Day
6/Sunday.

..Guyer.. 07/02/2024

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ACUS48 KWNS 030840
SWOD48
SPC AC 030839

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0339 AM CDT Wed Jul 03 2024

Valid 061200Z - 111200Z

...DISCUSSION...
...Mid-Atlantic...
For Saturday, severe thunderstorms are possible for parts of the
Mid-Atlantic as the upper-level trough moves northeastward through
the northern portion of the region. A cold front/surface trough
pendant to the surface low in southeastern Canada will be the focus
for convection by the afternoon. Models differ in the
strength/position of the surface low as well as the degree of
destabilization due to cloud cover.

...Central/southern High Plains...
With the broad trough to the north, the surface boundary is expected
to generally stall within the southern Plains and arc northwest into
the central/southern High Plains vicinity. Northwest flow aloft, on
Saturday and becoming stronger on Sunday, will promote some
potential for severe thunderstorm development. Both the GFS and
ECMWF hint at possible MCS development both days, but differ fairly substantially on the details. Sunday would appear to have greater
potential given that the upper trough will dig into the southern
High Plains.

...South Texas...
As TC Beryl continues north-northwestward, an increase in severe
weather potential may accompany its circulation as it eventually
impacts parts of South Texas. Per latest NHC forecasts, this could
occur as soon as this Sunday. However, uncertainty on the exact
positioning and strength of this activity is too high at this time
for highlights.

..Wendt.. 07/03/2024

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ACUS48 KWNS 040851
SWOD48
SPC AC 040850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Thu Jul 04 2024

Valid 071200Z - 121200Z

...DISCUSSION...
...D4/Sunday...
The upper-level trough will dig slightly farther south into Oklahoma
before lifting northeastward on Monday. For portions of the
central/southern Plains, both the ECMWF and GFS suggest that
convection will develop along the intersection of the cold and warm
front within a weak surface low. Similar to Saturday, moisture will
not be overly rich, but northward moisture return will be in
progress. Convection is forecast to grow upscale into an MCS and
move southward into the greater buoyancy. With differences in the
position and intensity of the surface low, as well as possible
impacts from convection on Saturday, predictability remains too low
for the introduction of 15% total severe probabilities.

TC Beryl continues to move towards the Yucatan Peninsula and is
expected to reach the Mexican coast south of Brownsville, TX on
Sunday per latest NHC forecasts. Some tornado risk is possible for
parts of South Texas, but magnitude and spatial extent of this risk
will depend on how much the TC restrengthens after interacting with
the Peninsula and where the system will actually track late this
weekend into early next week.

...D5/Monday and beyond...
The upper-level trough will slowly make progress into the Midwest
and eventually into the Ohio Valley and Northeast. While some severe
risk is possible ahead of this trough, questions regarding
destabilization and general lack of robust surface features during
the upcoming week keep confidence too low for highlights at this
time.

..Wendt.. 07/04/2024

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ACUS48 KWNS 050842
SWOD48
SPC AC 050841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Fri Jul 05 2024

Valid 081200Z - 131200Z

...DISCUSSION...
An upper-level trough will begin to lift northeastward out of the
southern Plains early next week. This feature will generally lose
amplitude slowly with time. The surface pattern will be nebulous
across the eastern half of the CONUS. By the middle of the week, the
mid-level jet may intensify in the Northeast and a surface low will
develop and move out of the CONUS by next Thursday. Given this
pattern, severe potential ahead of the upper trough appears rather
marginal.

In addition to the upper-trough, the remnants of TC Beryl are
currently forecast to turn eastward through Texas and into the
Mid-South early to late next week. While some severe potential could
develop ahead of this feature, predictability remains low at this
time.

..Wendt.. 07/05/2024

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ACUS48 KWNS 060824
SWOD48
SPC AC 060822

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0322 AM CDT Sat Jul 06 2024

Valid 091200Z - 141200Z

...DISCUSSION...
Predictability will remain low during the extended period. There may
be some increase in severe potential associated with the remnants of
TC Beryl mid to late next week. With some uncertainty in the track
and overall strength of the low-level wind fields, confidence in an
organized severe threat is low. Upper-level ridging is also expected
to expand eastward out of the West and encompass much of the CONUS
by late next week. The strongest flow aloft will be pushed northward
along the Canadian border. There are weak model signals for
convection within parts of the northern Plains late next week, but
confidence in the magnitude of risk is too low this far in advance.

..Wendt.. 07/06/2024

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ACUS48 KWNS 080829
SWOD48
SPC AC 080828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Mon Jul 08 2024

Valid 111200Z - 161200Z

...DISCUSSION...
Guidance consensus shows a mid-level trough de-amplifying over the
Northeast toward the end of the week as a pronounced mid-level ridge
builds over the CONUS this weekend into early next week. While
vertical wind profiles will remain weak overall across most of the
CONUS, strong mid-level flow associated with an embedded impulse
will pivot around the ridge and traverse the north-central CONUS
this weekend. Preceding this impulse will be a fetch of rich
low-level moisture beneath a plume of steep mid-level lapse rates
driven by the approach of an EML. Medium-range guidance agrees that
strong to extreme instability will develop ahead of the mid-level
impulse over the Upper MS Valley into the Great Lakes region.
However, substantial differences exist between the placement and
timing of the mid-level impulse and associated key surface features
(i.e. trough and boundaries). Given strong capping with the EML,
mesoscale forcing along low-level boundaries will likely be key to
initiating convection and supporting a severe threat.

With considerable uncertainty this far in advance, no severe
probabilities have been introduced. However, climatology suggests
that the aforementioned synoptic setup could support an appreciable
severe threat, including damaging-wind producing bow-echo MCSs. As
such, 15 percent probabilities may be introduced in future outlooks
for the upcoming weekend across portions of the Northern Plains into
the Great Lakes, if better model agreement in the timing of the
mid-level impulse, and associate surface boundaries, can be
achieved.

..Squitieri.. 07/08/2024

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ACUS48 KWNS 090900
SWOD48
SPC AC 090859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Tue Jul 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
Deterministic and ensemble guidance offers a strong consensus on a
general pattern shift involving deamplification of cyclonic flow
over the Great Lakes, Ohio Valley and northeast on day 4 (12th-13th)
through day 6 (14th-15th), but with a weaker version of the longwave
trough lingering in that region through the remainder of the outlook
period. Meanwhile, the Great Basin anticyclone is progged to expand
and shift eastward toward the central Rockies day 4 through day 6,
then deamplify over the central Plains. This process should
reinforce an EML over the western plateaus and expand it eastward
across the central Plains. As that occurs, west-northwesterly flow
aloft should set up between the northern Plains and Great Lakes,
mostly (but not entirely) north of a mean low-level frontal zone
occupying a corridor from the north-central High Plains to the lower Missouri/Ohio Valleys.

Strong lapse rates related to the EML, atop an enlarging area of
upper 60s to mid 70s F surface dewpoints (from both advection and evapotranspiration), will yield a high-CAPE parameter space near the
front. Provided it is not too far removed from that large buoyancy,
the northeastern rim of the stronger EML capping, aligned parallel
to the frontal instability gradient, may provide a favorable
corridor for development/propagation of organized,
severe-wind-producing MCS activity on at least one or two of those
days, from the weekend into early next week. Activity may be
supported by subtle shortwave troughs embedded in the largely
front-parallel flow. Confidence in shortwave details, and in which
day the cap is more likely to weaken enough to support suitable
initiation and upscale growth, currently is too low to assign
probabilities to a particular day in the series of somewhat similar
ones, pattern-wise.

..Edwards.. 07/09/2024

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ACUS48 KWNS 100852
SWOD48
SPC AC 100850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Wed Jul 10 2024

Valid 131200Z - 181200Z

...DISCUSSION...
An upper-level ridge will gradually shunt eastward from the southern
Rockies into the southern Plains and Lower MS Valley areas this
weekend into the middle of next week. Multiple pronounced mid-level
shortwave troughs and associated 500 mb speed maxima will pivot
around the upper ridge and traverse the Upper MS Valley into the
Northeast this weekend through early to mid next week. With adequate
low-level moisture and overall instability preceding the mid-level
troughs, severe thunderstorms are possible from the Upper MS Valley
to the Northeast at least this weekend, possibly into early next
week.

...Days 4-5 (Saturday-Sunday) - Upper MS Valley...
A 500 mb speed max will traverse the U.S./Canada border on Day 4
(Saturday) as surface lee troughing advects dewpoints well into the
70s F across the northern Plains into the Upper MS Valley. An EML
will also precede the mid-level speed max and overspread the rich
low-level moisture, contributing to 4000+ J/kg MUCAPE per latest
medium-range guidance consensus. Forcing for ascent will be modest
and capping will be present, though the approach of the speed max
may support convective initiation across the northern Plains into
the Great Lakes region. At the moment, too much disagreement exists
between medium-range guidance members regarding the placement of
convection to support the addition of severe probabilities for
Saturday.

Despite some timing issues, medium-range guidance is in better
agreement in depicting a mid-level impulse and accompanying wave of
deep-moist convection traversing the Upper MS Valley area on Day 5
(Sunday). There is some concern that preceding convection from Day 4
could promote stability over portions of the Upper MS Valley into
the Great Lakes. Nonetheless, both the ECMWF and GFS agree that the
EML will continue regenerate from the southwest, focusing strong to
potentially extreme instability into portions of this region. At the
moment, it appears the best chance for severe convection (including
the possibility of an organized, sustained MCS) would be over
central MN into WI Sunday afternoon or evening, warranting the
introduction of 15 percent severe probabilities. However, these
probabilities may need to be considerably adjusted based on
timing/placement changes of key mesoscale features, or to account
for any impacts from preceding convection in later outlooks.

...Days 6-8 (Monday-Wednesday) - Northern Plains to the Northeast...

The first mid-level impulse will eject into the Northeast on Day 6
(Monday). Some instability will precede this impulse, and
medium-range guidance suggests that convective precipitation is
possible. However, given limited deep-layer shear and ascent,
confidence is too low to provide severe probabilities. Meanwhile,
medium-range guidance consensus hints at convective development over
parts of the northern Plains toward the Great Lakes on Monday as a
second mid-level impulse impinges on the region. Though guidance
consensus shows adequate overlapping shear and instability to
support severe storms, relatively weak forcing for ascent and
convective signals in the guidance preclude severe probabilities. By
Days 7-8 (Tuesday-Wednesday), the second approaching mid-level
trough will amplify while overspreading the Great Lakes, supporting
a southward-surging cold front from the MS Valley into the
northeast. Forcing for ascent and accompanying buoyancy suggests
severe thunderstorms are possible from the MS Valley to New England.
However, details on frontal timing and placement this far in advance
are too nebulous for severe probabilities at this time.

..Squitieri.. 07/10/2024

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ACUS48 KWNS 110851
SWOD48
SPC AC 110850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Thu Jul 11 2024

Valid 141200Z - 191200Z

...DISCUSSION...
An upper-level ridge will remain in place over much of the western
and central CONUS through at least early next week. Multiple
mid-level impulses are expected to traverse the anticyclonic flow
over the northern CONUS through at least Days 4-5 (Sunday-Monday).
These impulses may be accompanied by multiple rounds of strong to
severe thunderstorms given continued low-level WAA/moisture
advection along the eastern periphery of a regenerating EML. By days
6-7 (Tuesday-Wednesday), a mid-level trough will amplify over the
Great Lakes, with a surface cold front expected to sweep southward
across the northern Plains into the Northeast, promoting showers and thunderstorms (perhaps strong to severe), but also clearing out the
low-level moisture, EML, and associated buoyancy in the process.

...Days 4-5 (Sunday-Monday)...
Medium-range guidance consensus shows a mid-level impulse
approaching the Great Lakes region from the northern Plains on
Sunday (albeit later than earlier model runs). While both the latest
ECMWF and GFS agree on the mid-level impulse overspreading the nose
of the WAA (and associated 3000-4000 J/kg MUCAPE) over the Upper MS
Valley on Sunday, the later arrival of the mid-level impulse past
peak afternoon heating results in a complex forecast. The GFS
depicts potential convection over the northern Great Lakes by late afternoon/early evening while the ECMWF develops precipitation over central/southern MN that rapidly progress to the WI/IL border. While
it is unclear which scenario will unfold, both regimes involve
organized convection traversing an axis of strong to extreme
instability amid adequate deep-layer shear to support a severe
threat. This includes the possibility of a severe-wind producing
MCS, warranting a broad 15 percent area. Substantial modifications
may be needed to this highlight in later outlooks as mesoscale
details and associated placement of key baroclinic boundaries
becomes evident.

The latest ECMWF and GFS depicts a more pronounced mid-level trough
traversing the Upper MS Valley by afternoon peak heating on Day 5
(Monday). Continued low-level moisture advection from the south,
beneath a regenerating plume of steep mid-level lapse rates from the
west, will support another day of strong to extreme instability
overspreading the Upper Midwest. This time, stronger deep-layer
shear with the better-timed mid-level impulse will coincide with the instability axis, fostering an environment favorable for severe
storms. Given impacts from Day 4 (Sunday) convection, it is unclear
how and where mesoscale low-level boundaries will become established
over the Midwest, and these will be key to supporting a severe
threat (including the possibility of severe wind-producing bow-echo
MCSs). 15 percent highlights have been added over the general area
where both the GFS and ECMWF agree on precipitation occurring with
overlapping favorable vertical wind shear and strong/extreme
instability. Like Sunday though, the highlights provided for Monday
will likely need substantial modification based on later-known
placement of important mesoscale meteorological features.

...Days 6-7 (Tuesday-Wednesday)...
ECMWF and GFS are in general agreement in thunderstorms initiating
along and ahead of a surface cold front, anywhere from the northern
Plains to the Northeast states in the Days 6-7 (Tuesday-Wednesday)
time frame. These storms would traverse a buoyancy axis, possibly
becoming strong or even severe in the process. However, great
uncertainty exists on precisely where and when the greatest severe
threat would materialize, since there is more disagreement among
medium-range guidance members compared to earlier days. Furthermore,
details on severe placement and timing still hinge on the evolution
of earlier thunderstorm events (i.e. where baroclinic boundaries are
left behind). When taking into account both model disagreements and uncertainties of preceding convective influences, severe
probabilities have been withheld this outlook.

..Squitieri.. 07/11/2024

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ACUS48 KWNS 120848
SWOD48
SPC AC 120846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Fri Jul 12 2024

Valid 151200Z - 201200Z

...DISCUSSION...
Western CONUS upper ridging is forecast to persist through at least
the middle of next week, with notable amplification anticipated on
D5/Tuesday and D6/Wednesday. Subtropical ridging will likely persist
across the Southeast states during this time frame as well, while
broadly cyclonic flow continues north of this subtropical ridging
from the northern Plains to the Northeast.

Medium-range guidance is in relatively good agreement that a
shortwave trough will progress through the cyclonic flow across the north-central/northeast CONUS, moving from the Upper Midwest through
the Upper Great Lakes on D4/Monday. Thunderstorms may be ongoing
early D4/Monday across the Upper Midwest ahead of this shortwave,
with some potential for these storms to continue progressing
southeastward into the strong buoyancy expected downstream. Severe
gusts could occur with the resulting convective line if this
scenario is realized, and 15% severe probabilities were maintained
for this outlook. The outlook area was shifted slightly northward to
account for changes within the most recent guidance.

Aforementioned shortwave trough is forecast to continue eastward
through the Ohio Valley and Northeast on D5/Tuesday. Thunderstorms
are possible along this front, but shear will be modest and the severe-thunderstorm coverage is currently expected to be low.

The cold front will likely continue southward/eastward on
D6/Wednesday and D7/Thursday, but model guidance differs on the
speed of its southward/eastward progression. Some limited severe
potential may linger across the Northeast on D6/Wednesday if the
slower frontal progression is realized. By D7/Thursday, the front
will likely extend from northern southern Plains through the Mid MS
and TN Valleys, and into the Mid-Atlantic, becoming displaced from
the stronger westerly flow aloft.

..Mosier.. 07/12/2024

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ACUS48 KWNS 130819
SWOD48
SPC AC 130818

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0318 AM CDT Sat Jul 13 2024

Valid 161200Z - 211200Z

...DISCUSSION...
Western CONUS upper ridging is expected to build throughout much of
the week, with this expansive ridging likely extending into much of
western Canada by the end of the week. Modest upper troughing is
anticipated over much of the central and eastern CONUS. A series of
shortwave troughs will likely move through this upper troughing,
helping to push a cold front gradually southward/eastward from
D4/Tuesday through D7/Friday.

Thunderstorms are anticipated along the front, with strong buoyancy
and moderate shear potentially supporting strong to severe storms
from the OH Valley into the Northeast on D4/Tuesday. Some severe
potential may linger across the Northeast on D5/Wednesday before the
front clears the region. After D5/Wednesday, progression of the
front will displace the better low-level moisture south of the
stronger flow aloft, limiting the severe-storm potential across much
of the central and eastern CONUS from D6/Thursday through
D8/Saturday. The only exception is across the High Plains, where
modest low-level moisture beneath vertically veering wind profiles
could support a few strong to severe storms.

..Mosier.. 07/13/2024

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ACUS48 KWNS 140827
SWOD48
SPC AC 140826

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CDT Sun Jul 14 2024

Valid 171200Z - 221200Z

...DISCUSSION...
Expansive upper ridging is expected to be in place across much of
western North America on D4/Wednesday, with this ridging expected to
persist through the weekend. Upper troughing will likely extend from
northern Quebec through Ontario, the Upper Great Lakes, and the Mid
MS Valley early D4/Wednesday. Primary portion of this upper trough
is forecast to gradually shift eastward across the remainder of
Ontario and the Upper Great Lakes on D4/Wednesday and the Northeast
on D5/Thursday, but modest upper troughing is expected to remain in
place over much of the eastern CONUS into the weekend.

At the same time, a cold front will gradually push
southward/southeastward across the central Plains, OH Valley, and
Northeast on D4/Wednesday and northern part of the southern Plains,
Mid-South, and TN Valley on D5/Thursday. Some limited severe
potential may exist across the Northeast on D4/Wednesday before the
front clears the region. After D4/Wednesday, progression of the
front will displace the better low-level moisture south of the
stronger flow aloft, limiting the severe-storm potential across much
of the central and eastern CONUS through the weekend. The only
exception is across the High Plains, where modest low-level moisture
beneath vertically veering wind profiles could support a few strong
to severe storms each afternoon.

..Mosier.. 07/14/2024

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ACUS48 KWNS 150853
SWOD48
SPC AC 150852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Mon Jul 15 2024

Valid 181200Z - 231200Z

...DISCUSSION...
Medium-range guidance continues to show that the upper ridging
expected to be in place across the western CONUS early D4/Thursday
will persist through the weekend and into early next week while also
building into western Canada. Upper troughing is expected to persist
across the central and eastern CONUS through the weekend as well.
Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features
across the High Plains.

A cold front will likely stretch from the Mid-Atlantic through north
Texas. This front is expected to become increasingly diffuse on
D4/Thursday and D5/Friday as it moves only slightly southward.
Thunderstorms are possible along this boundary on each day, but weak
vertical shear should keep the severe potential low.

Aforementioned northwesterly flow aloft will help support some
severe potential across the High Plains, where modest low-level
moisture beneath vertically veering wind profiles could support a
few strong to severe storms each afternoon on D4/Thursday through
D6/Saturday. After D6/Saturday, the upper ridge may shift westward,
placing the northwesterly flow over the higher terrain and likely
limited the severe potential.

..Mosier.. 07/15/2024

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ACUS48 KWNS 160834
SWOD48
SPC AC 160833

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CDT Tue Jul 16 2024

Valid 191200Z - 241200Z

...DISCUSSION...
The extensive upper ridging expected to be in place from the
Southwest into western Canada early D4/Friday is forecast to persist
through the weekend and into early next week. Modest downstream
upper troughing across the central and eastern CONUS is expected to
persist as well, resulting in little change in the overall upper
pattern across the CONUS from D4/Friday into D8/Tuesday.

Moderate northwesterly flow aloft is expected between these two
features, extending across the northern and central High Plains on
D4/Friday and D5/Saturday before then shifting westward as the
overall upper pattern shifts slightly westward. This northwesterly
flow aloft could support some severe potential across the northern
and central High Plains, where modest low-level moisture beneath
vertically veering wind profiles could support a few strong to
severe storms on D4/Friday and D5/Saturday.

..Mosier.. 07/16/2024

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ACUS48 KWNS 170827
SWOD48
SPC AC 170825

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0325 AM CDT Wed Jul 17 2024

Valid 201200Z - 251200Z

...DISCUSSION...
Extensive upper ridging is expected to extend from the Southwest
into western Canada on D4/Saturday morning. This upper ridging is
forecast to persist throughout the weekend and into early next week,
shifting gradually westward during this period. Modest downstream
upper troughing across the central and eastern CONUS is expected to
persist through the weekend and into next week as well, with some
westward shift of this troughing also possible. In general, no
substantial changes to the upper pattern are currently anticipated
from D4/Saturday to D8/Wednesday.

Moderate northwesterly flow aloft is expected between these two
features, extending across the northern and central High Plains on
D4/Saturday before then shifting westward. Current guidance suggests
a low-amplitude, convectively augmented shortwave trough may move
through this northwesterly flow across central Plains.
Predictability of these types of shortwaves is low at this forecast
range, but it would provide the lift needed for storm development if
realized. Lift attendant to this shortwave and/or low-level
convergence along the lee trough could support thunderstorms across
the northern and central High Plains and adjacent Plains. Modest
low-level moisture beneath vertically veering wind profiles could
result in some strong to severe thunderstorms.

The severe risk is expected to be lower from D5/Sunday into
D8/Wednesday, as the northwesterly flow aloft shifts westward and
weak upper flow prevails across much of the central and eastern
CONUS.

..Mosier.. 07/17/2024

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ACUS48 KWNS 180842
SWOD48
SPC AC 180841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Thu Jul 18 2024

Valid 211200Z - 261200Z

...DISCUSSION...
Extensive upper ridging is expected to extend from the Southwest
into western Canada on D4/Sunday morning. This upper ridging is
forecast to persist into the middle of next week, while gradually
shifting westward over time. Modest downstream upper troughing
across the central and eastern CONUS is expected to persist through
into the middle of next week as well, with some westward shift of
this troughing also possible. In general, no substantial changes to
the upper pattern are currently anticipated from D4/Sunday to
D8/Thursday.

Westward shift in the upper pattern will likely place the stronger northwesterly flow aloft between the ridging and troughing over the
higher terrain of the western CONUS, limiting the severe potential.
Farther east, a belt of enhanced mid-level southwesterly flow aloft
may strengthen from D5/Monday through D7/Wednesday as subtropical
ridging building into the southeast CONUS along on the southeastern
periphery of the upper trough. Low-level moisture will gradually
build northward, allowing for some overlap between the enhanced
southwesterlies and modest buoyancy. However, even with this
overlap, the severe potential appears low, with both buoyancy and
vertical shear forecast to remain modest.

..Mosier.. 07/18/2024

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ACUS48 KWNS 190851
SWOD48
SPC AC 190849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Fri Jul 19 2024

Valid 221200Z - 271200Z

...DISCUSSION...
The overall pattern will not change much during the Day 4-8 period.
An upper ridge over the western states will gradually shift east
into the Plains around Days 7-8/Thu-Fri. Meanwhile, a mean upper
trough will persist across the eastern U.S., with some eastward
progression of an embedded shortwave trough from the upper Great
Lakes toward the Northeast around mid to late week. Mid/upper flow
will remain modest. Given an overall stagnant upper pattern, a
somewhat nondescript surface pattern lacking any appreciable
cyclogenesis is forecast. While a typically moist and unstable
summertime airmass will be in place east of the Rockies,
severe-thunderstorm chances appear low.

..Leitman.. 07/19/2024

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ACUS48 KWNS 200843
SWOD48
SPC AC 200841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Sat Jul 20 2024

Valid 231200Z - 281200Z

...DISCUSSION...
An upper ridge will persist over the western U.S. through the middle
of the week before slowly shifting east into the Plains around Day 6
or 7/Thu or Fri. Meanwhile, upper troughing will prevail over the
eastern CONUS throughout the Day 4-8 period. While a moist airmass
typical of summertime will prevail over much of the CONUS east of
the Rockies, weak mid/upper flow will likely limit organized severe thunderstorm potential, especially given a lack of any stronger
surface cyclogenesis and upper shortwave impulses.

..Leitman.. 07/20/2024

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ACUS48 KWNS 210829
SWOD48
SPC AC 210827

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0327 AM CDT Sun Jul 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
A somewhat more progressive upper-level pattern will emerge during
the Day 4-8/Wed-Sun period. The upper trough over the Great
Lakes/Midwest early in the period will shift east across the
Northeast and Mid-Atlantic through Day 6/Fri. As this occurs, the
western upper ridge will overspread the central portion of the CONUS
while a series of upper shortwave troughs move across the northern
Rockies and Pacific Northwest.

The Great Lakes upper trough will deepen on Day 4/Wed, and a cold
front will sag south/southeast across Lower MI and northern
IL/IN/OH. This could focus a corridor of strong thunderstorm
potential, but vertical shear will remain modest and training
thunderstorm activity may favor heavy rain rather than organized
severe. As the upper trough migrates east toward the Northeast Days 5-6/Thu-Fri, a surface cold front will spread across the Midwest
into the Mid-Atlantic and New England. Deep-layer flow is not
forecast to be very strong, but a very moist airmass will be in
place, and some potential for strong thunderstorms is possible near
the end of the work week from VA northward into southern New
England.

Overall, organized severe potential appears low during the Day 4-8
period.

..Leitman.. 07/21/2024

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ACUS48 KWNS 220801
SWOD48
SPC AC 220800

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 AM CDT Mon Jul 22 2024

Valid 251200Z - 301200Z

...DISCUSSION...
An upper trough will move over the Northeast on Day 4/Thu and
persist, albeit weakening with time, for much of the Day 4-8 period.
Surface high pressure will build in the wake of a cold front moving
across the Northeast on Thursday, and also persist into early next
week. Some severe thunderstorm potential could develop over the
Northeast states on Thursday as the cold front pushes east. However,
timing of the front may be unfavorable with the diurnal cycle, and
confidence is too low to include severe probabilities.

Meanwhile, an upper ridge will overspread much of the Plains, while
a series of upper shortwave troughs move across the Pacific
Northwest vicinity. Boundary layer moisture will increase beneath
the upper ridge over the Plains. With the upper trough and surface
high over the Midwest/Northeast blocking progression of the upper
ridge over the Plains, daily surface trough/weak low development is
expected over the northern/central High Plains vicinity. However,
under the influence of an amplified upper ridge, thunderstorm
development each day is uncertain given a lack of large-scale ascent
and likely capping concerns.

Overall, severe thunderstorm potential appears low during the Day
4-8 period.

..Leitman.. 07/22/2024

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ACUS48 KWNS 230847
SWOD48
SPC AC 230846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Tue Jul 23 2024

Valid 261200Z - 311200Z

...DISCUSSION...
Upper ridging will spread across parts of the Plains and eastern
states, while the subtropical high develops westward over the
southern tier of the U.S. during the Day 4-8/Fri-Tue period. This
will suppress severe thunderstorm potential for much of the CONUS.
The exception will be a potentially more active period for parts of
the northern Plains into the Upper Midwest due to a series of upper
shortwave troughs migrating across the Canadian Prairies and parts
of the northern Plains/Upper Midwest through the forecast period.

Surface high pressure over the Great Lakes and periodic surface low
development over the northern High Plains will maintain a baroclinic
zone over the Upper Midwest. As a result, southerly low-level flow
will keep a seasonally moist airmass in place across the eastern
Dakotas and Mid-MO Valley east to the Mid/Upper MS Valley. Some
severe thunderstorm potential could develop around Day 4 Fri as the
first upper shortwave trough moves across the Canadian Prairies.
However, stronger vertical shear and large scale ascent will be
focused north of the international border. Another weaker, but
further south shortwave trough will traverse the northern Plains
vicinity on Day 6/Sun before a somewhat stronger wave migrates
through westerly flow toward Day 8/Tue.

While various forecast guidance generally depicts this more
progressive northern stream pattern, details in timing of each wave,
as well as differences in the strength of the central U.S. upper ridge/subtropical high vary greatly. As a result, confidence is too
low to include 15 percent probabilities at this time.

..Leitman.. 07/23/2024

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ACUS48 KWNS 240830
SWOD48
SPC AC 240828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Wed Jul 24 2024

Valid 271200Z - 011200Z

...DISCUSSION...
The beginning of the Day 4-8 period will see the central U.S. upper
ridge shunted east over the eastern third of the CONUS. A weak upper
shortwave trough within broader westerly flow will develop northeast
from the Ozarks toward the Great Lakes/Midwest through Day 5/Sun.
The remainder of the period will be characterized by a building
upper ridge over the Rockies and shifting east over the Plains Days 6-8/Mon-Wed. The late period upper ridge will be flanked by
shortwave troughs over the Pacific Northwest and the lower Great Lakes/Northeast. Overall, deep-layer flow will remain weak in this
regime.

However, a reservoir of rich boundary layer moisture will persist
from eastern portions of the Plains to the MS Valley. Large-scale
ascent will remain nebulous, and capping beneath the upper ridge may
ultimate limit severe potential. However, mesoscale features not
well resolved at long time scales may support some risk of severe
thunderstorms across the warm sector given rich boundary layer
moisture and large instability in a northwesterly flow regime on the
eastern periphery of the upper ridge Day 6/Mon-Day 8/Wed. Confidence
is too low to introduce 15 percent probabilities at this time.

..Leitman.. 07/24/2024

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ACUS48 KWNS 250836
SWOD48
SPC AC 250834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0334 AM CDT Thu Jul 25 2024

Valid 281200Z - 021200Z

...DISCUSSION...
A weak upper trough will migrate across the Midwest early in the
forecast period. However, weak deep-layer flow and relatively modest large-scale ascent may limit severe potential. Generally
low-amplitude upper troughing will then prevail across the eastern
third of the CONUS through much of the work week.

Meanwhile, an expansive upper ridge centered over the Rockies/High
Plains vicinity will persist for much of the Day 4-8 period. Some
severe potential is possible in a northwesterly flow regime over the
Mid-MO to Mid-MS Valley around Days 5-6/Mon-Tue, but this risk would
largely be driven by mesoscale factors not well resolved at longer
time periods.

Late in the period, forecast guidance suggests a shortwave trough
may develop eastward atop the upper ridge in the vicinity of the
northern Plains. This break down of the upper ridge amid a very
moist and unstable boundary layer would be a favorable pattern for
potential MCS development around Day 7 or 8/Wed or Thu. Confidence
in this scenario remains too low to include probabilities at this
time, but may become necessary in subsequent outlooks.

..Leitman.. 07/25/2024

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ACUS48 KWNS 270845
SWOD48
SPC AC 270844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Sat Jul 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
A ridge over the central CONUS will break down toward the middle of
next week which will likely result in some severe weather from the
northern Plains to the Ohio Valley D4/Tuesday and D5/Wednesday.
Toward the end of the week and into next weekend, a strong
upper-level ridge will build across the western CONUS with somewhat
lower severe weather concerns across the CONUS.

...Day4/Tue - Northern Plains to the Midwest...
A broad reservoir of 70F dewpoints are expected to exist from the
Canadian border into the Midwest and Ohio Valley on Tuesday. This
will result in an extended corridor of very unstable conditions
along and south of a frontal zone. Some moderate (30-35 knot)
mid-level northwesterly flow is expected along this frontal zone.
This pattern may support one or more severe MCSs on Tuesday.
However, a lack of a focused/strong low-level jet and weak,
mesoscale, mid-level shortwave troughs make predictability
challenging at this range. Therefore, no probabilities are warranted
at this time.

...D5/Wed - Midwest to the Ohio Valley and central Appalachians...
A diffuse frontal zone with strong instability will likely exist
from the Midwest to Ohio Valley and central Appalachians on
Wednesday. Some threat for severe MCS development will be likely
across this corridor, but the lack of a clear forcing mechanism
precludes probabilities at this time. The upper-level ridge centered
across the central CONUS will start to break down Wednesday night.
This should result in moderate forcing for ascent amid a very
unstable airmass. Therefore, some overnight severe weather threat
may exist in the Upper Midwest, particularly across southern
Minnesota where there is moderate agreement between the GFS and
ECMWF for the best upper-level forcing. If this ridge break down can
occur 6-12 hours earlier and the stronger forcing could coincide
with peak heating, a greater severe weather threat may evolve across
portions of the Upper Midwest.

..Bentley.. 07/27/2024

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ACUS48 KWNS 280902
SWOD48
SPC AC 280900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Sun Jul 28 2024

Valid 311200Z - 051200Z

...DISCUSSION...
A broad, low-amplitude mid-level ridge is expected to break down on Day4/Wednesday and Day5/Thursday. This may result in some severe
weather across portions of the Midwest. Late this week and into the
weekend, ridging will amplify across the western CONUS. Depending on
the exact evolution of the building upper-level trough, some severe
weather threat may persist across the northern Plains. However, an
area of high pressure is expected to move south out of Canada over
the weekend and scour the higher quality moisture which should
result in less instability than early this week.

...D4/Wednesday and D5/Thursday - Midwest...
Uncertainties remain in the exact evolution of the upper-level ridge
breakdown on Wednesday and Thursday which may significantly impact
the location and intensity of any severe weather threat. A reservoir
of strong instability and steep lapse rates is expected in the
Midwest/Upper Midwest with increasing mid-level flow across the
region. Where storms develop within this environment, severe weather
is likely. However, aforementioned uncertainties preclude the need
for severe weather probabilities at this time.

..Bentley.. 07/28/2024

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ACUS48 KWNS 290827
SWOD48
SPC AC 290826

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CDT Mon Jul 29 2024

Valid 011200Z - 061200Z

...DISCUSSION...
A mid-level trough, likely near the Upper Midwest Thursday morning,
will slowly move east through the end of this week and the weekend
as a large amplitude ridge builds over the western CONUS. This slow
moving trough will be the primary feature associated with potential
severe weather during the extended forecast period.

On D4/Thu, a large cluster of storms will likely be ongoing in the
western Great Lakes in response to the forcing from the mid-level
trough and moderately strong isentropic ascent. A very moist airmass
(mid 70s dewpoints) will likely remain on the southern/southwest
extent of any ongoing convection. This will likely be the focus for
potential severe weather threat across Illinois/Indiana/Ohio on
Thursday. Strong instability will be present, however shear will be
somewhat weak, except for portions of Illinois where mid-level flow
will strengthen during the late afternoon/evening. There is still
uncertainty regarding the timing and amplitude of this mid-level
trough. Therefore, no severe weather probabilities will be added at
this time.

As the mid-level trough continues east on D5/Fri and into the
weekend, moisture quality, and thus instability, is forecast to
weaken. In addition, the slowing/deamplifying nature of the
mid-level trough will result in weakening mid-level flow. Therefore,
while some isolated/widely scattered severe weather threat may occur
across portions of the eastern CONUS, a more organized severe
weather threat appears unlikely.

..Bentley.. 07/29/2024

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ACUS48 KWNS 300856
SWOD48
SPC AC 300854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Tue Jul 30 2024

Valid 021200Z - 071200Z

...DISCUSSION...
On Friday and into the weekend, a mid-level trough will slow and
eventually stall across the eastern CONUS. Given remnant moisture,
expect widespread thunderstorm activity. However, severe weather
should be limited by weak shear in the region.

A large-amplitude mid-level ridge which is forecast to build across
the western CONUS on Thursday and Friday will start to deamplify
over the weekend as a series of mid-level shortwave troughs traverse
British Columbia and Alberta. The exact evolution of the pattern
over the weekend and beyond remains uncertain. There is consensus
for multiple mid-level troughs to move through the northern CONUS
with at least some lee troughing across the northern Plains. Some
severe weather is possible with any of these passing impulses.
However, uncertainty remains too high at this time for severe
weather probabilities.

..Bentley.. 07/30/2024

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ACUS48 KWNS 310902
SWOD48
SPC AC 310901

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0401 AM CDT Wed Jul 31 2024

Valid 031200Z - 081200Z

...DISCUSSION...
The extended period will begin with a large amplitude upper-level
ridge across the western CONUS. This ridge will gradually breakdown
on Sunday and Monday with more of a flat ridge by the middle of next
week. Persistent northwesterly flow across the Northern Plains/Upper
Midwest during the extended forecast period may result in some
isolated severe weather threat. However, moisture in the Northern
Plains will lack a Gulf of Mexico connection and thus, will likely
be somewhat low quality, at least initially.

Early next week, as lee troughing returns to the Plains and the
low-level jet strengthens, the severe weather threat may increase
somewhat. Overall, upper-level ridging and no clear strong troughs
during the extended period, suggests any severe weather threat that materializes will likely remain somewhat localized this weekend and
early next week.

..Bentley.. 07/31/2024

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ACUS48 KWNS 010849
SWOD48
SPC AC 010848

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CDT Thu Aug 01 2024

Valid 041200Z - 091200Z

...DISCUSSION...
The extended forecast period will feature an upper-level ridge
centered near the Continental Divide with northwesterly flow aloft
from the northern Plains to the East Coast. Severe weather may be
possible any day within this corridor within a pocket of remnant
moisture along/near the frontal zone across the region, and shear
which would support organized severe weather. However, the pocket of instability is relatively narrow given a drier, more continental
airmass so the south of this frontal zone with persistent northerly
flow and a lack of a consistent Gulf moisture feed. In addition, any
mid-level shortwave troughs embedded within the northwesterly flow
will be mesoscale in nature and thus, the details cannot be resolved
at this range.

In addition, the Gulf Coast, Florida, and the Georgia/south Carolina
coast will need to be monitored for potential impacts from a
tropical wave which according to the National Hurricane Center,
could develop into a tropical cyclone late this weekend or early
next week. If an organized tropical system does develop, some
severe-weather threat may materialize.

..Bentley.. 08/01/2024

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ACUS48 KWNS 020846
SWOD48
SPC AC 020844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Fri Aug 02 2024

Valid 051200Z - 101200Z

...DISCUSSION...
Medium-range models indicate that mid-level flow across the northern mid-latitudes may trend less amplified by the middle of next week,
as a mid-level low over northern Quebec weakens/redevelops eastward
into the northwestern Atlantic and a prominent high over
northwestern Canada becomes suppressed. As this occurs, it appears
that low-level cooling and drying may advance southward toward the
Southeast and lower Mississippi Valley, beneath generally weak flow
associated with mid/upper ridging.

Developments across the West remain more uncertain, but it does
appear that persistent mid-upper ridging will become suppressed.
While it is possible that large-scale mid-level troughing may evolve
across the Pacific Northwest and Canadian/northern U.S. Rockies
vicinity, it is not clear that this will be accompanied by potential
for more than isolated strong to severe thunderstorm development
across the northern Intermountain region into northern U.S. Rockies.

..Kerr.. 08/02/2024

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ACUS48 KWNS 030902
SWOD48
SPC AC 030900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Sat Aug 03 2024

Valid 061200Z - 111200Z

...DISCUSSION...
Models suggest that seasonably high moisture content will linger in
a plume along/east of a weak mid-level trough/shear axis, offshore
of the northern Atlantic coast into the southern Atlantic coast
vicinity, as northerly flow leads to continued general drying
elsewhere to the east of the Rockies. It appears possible that a
lingering tropical cyclone, initially centered near/offshore of the
southern Atlantic coast at the outset of the period, remains the
primary potential focus for severe weather, and even this may remain
rather limited. Within weak steering flow, the forecast motion of
this system remains somewhat uncertain. Guidance suggests that a
continuing tropical storm may shift back inland across the Carolinas
by Wednesday or Thursday, before tending to migrate
north-northeastward. While it is possible that this may be
accompanied by at least some continuing tornado potential, this risk
seems likely to remain generally low. Severe probabilities are
being maintained at less than 15 percent through this period.

..Kerr.. 08/03/2024

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ACUS48 KWNS 040900
SWOD48
SPC AC 040859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Sun Aug 04 2024

Valid 071200Z - 121200Z

...DISCUSSION...
Medium-range guidance suggests that fairly prominent mid-level
ridging will be maintained through this period across much of the
Southwest and southern Rockies through the southern Great Plains.
Upstream, it appears that mid-level troughing may become established
near the U.S. Pacific coast by next weekend. Otherwise, the
evolution of troughing downstream of a prominent mid-level high
initially shifting across the Canadian Northwest Territories is more
unclear. Some amplification may eventually contribute to the
northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level
circulation center likely shifts back inland across coastal areas
into the southern South Carolina vicinity by Thursday. If this were
to occur, it probably would be accompanied by at least some risk for
convection capable of producing tornadoes into the Mid Atlantic
coast vicinity. However, it is not clear that this potential will
support more than low severe probabilities, and severe weather
elsewhere across the U.S. still appears likely to remain limited
through this period.

..Kerr.. 08/04/2024

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ACUS48 KWNS 060900
SWOD48
SPC AC 060859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Tue Aug 06 2024

Valid 091200Z - 141200Z

...DISCUSSION...
Medium-range guidance indicates that a significant mid-level trough
and embedded cyclonic circulation, evolving near the Upper
Midwest/Great Lakes region by the beginning of the period, will
progress eastward across much of the Northeast by late this weekend.
As this occurs, it appears that the remnants of Debby will
accelerate into and northeast of the northern Mid Atlantic region on
Saturday.

Although the degree of interaction between these features remains
unclear, significant strengthening of southerly
lower/mid-tropospheric flow appears possible within a plume of
tropical moisture advecting northward in advance of deepening
surface troughing, across the northern Mid Atlantic and
Hudson/Champlain Valleys through New England Saturday through
Saturday night. Warm mid-levels likely will limit deep-layer
instability; but low-level buoyancy, forcing for ascent and shear
might become conducive to organizing low-topped convection. In the
presence of mean cloud-bearing layer flow possibly on the order of
40-50+ kt, and boundary-layer dew points in the lower/mid 70s,
damaging wind gusts and perhaps a few tornadoes will be possible if
this scenario unfolds. Due to lingering uncertainties, severe
probabilities are being maintained at less than 15 percent. But
this could change in later outlooks for this coming Saturday.

..Kerr.. 08/06/2024

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ACUS48 KWNS 070902
SWOD48
SPC AC 070900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Wed Aug 07 2024

Valid 101200Z - 151200Z

...DISCUSSION...
Medium-range guidance indicates that the initially prominent
higher-latitude mid-level ridging emerging from the Canadian
Northwest Territories will gradually become suppressed through this
period. Although there is notable spread concerning the downstream acceleration of the initially significant mid-level low to its
southeast, it appears that larger-scale mid-level troughing will
slowly shift eastward in positively tilted fashion, through the St.
Lawrence Valley and lower Great Lakes region by late this coming
weekend, through the Northeast and Canadian Maritimes by the middle
of next week.

In advance of the troughing, Debby's remnant surface low may
interact with a surface cold front advancing to the east of the
lower Great Lakes/upper Ohio Valley, before perhaps merging into the
primary surface cyclone across southern Quebec by Saturday. Models
have varied concerning these developments, but tropical pre-frontal
moistening in the presence of intensifying deep-layer southerly wind
fields might be accompanied by an evolving low-topped convective
band with potential to produce damaging wind gusts near/east of the Hudson/Champlain Valleys through New England. Due to lingering
uncertainties severe probabilities are begin maintained at less than
15 percent, but this could change in later outlooks for Saturday.

Otherwise, the potential for severe weather elsewhere across the
U.S. late this coming weekend into the middle of next week appears
likely to be remain limited by the lack of stronger boundary-layer destabilization.

..Kerr.. 08/07/2024

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ACUS48 KWNS 080858
SWOD48
SPC AC 080856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Thu Aug 08 2024

Valid 111200Z - 161200Z

...DISCUSSION...
Medium-range model output exhibits considerable spread concerning
short wave developments within the evolving mid/upper flow through
this period. In general, though, it appears that an initially
significant, positively tilted mid-level trough will become
increasingly sheared while progressing through a confluent regime
across and east of the North Atlantic Seaboard late this coming
weekend into early next week. In its wake, generally weak zonal
flow across the U.S. may undergo some amplification by the middle to
later portion of next week, including rising mid-level heights to
the lee of the Rockies, downstream of digging mid-level troughing
near the Pacific coast.

As this regime evolves, boundary-layer dew points are likely to
gradually increase beneath the mid-level ridge, probably back into
the 70s F across parts of the lower through middle Missouri Valley.
Across the middle Missouri Valley, perhaps into lower Missouri
Valley, it appears that this may occur beneath an east-southeastward
advecting plume of warm elevated mixed-layer air, which may
contribute to increasing probabilities for mixed-layer CAPE in
excess of 2000 J/kg by next Wednesday or Thursday.

While there may be some potential for strong thunderstorm activity,
initiating to the lee of the northern Rockies and Front Range, to
grow upscale and organize while progressing into this environment,
this likely will hinge on forcing accompanying sub-synoptic
perturbations progressing around the ridge. Given the
low-predictability of these features at this extended time frame,
severe probabilities still appear generally low through this period.

..Kerr.. 08/08/2024

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ACUS48 KWNS 090820
SWOD48
SPC AC 090819

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CDT Fri Aug 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
In mid/upper levels, a zonally elongated anticyclone will build
laterally from the southern Plains into the Southwest and Gulf Coast
region through much of the day-4-8 period. A general weakness in
heights should persist over parts of CA and the lower Colorado River
Valley region -- intermittently connected to northern-stream
troughing over the Pacific Northwest and western Canada, and to the
subtropical easterlies over MX. Low-amplitude mean ridging should
build northward across the Rockies to the northern Rockies/northern
High Plains region, but based on deterministic GFS/ECMWF and their
ensembles, not intense enough to preclude penetration by a series of
mostly low-amplitude/low-predictability shortwaves emanating from
the Northwest troughing.

Downstream, zonal to northwesterly and largely difluent flow will
prevail over much of the northern Plains, Midwest, Great Lakes, and
Ohio Valley. Even after the southeastern Canada/northeastern CONUS
synoptic trough departs the region day-4, the preceding frontal zone
will remain well-removed to the south, across the southeastern CONUS
to Missouri Valley, as a series of trailing shortwaves reinforce
somewhat lower-amplitude troughing in the Great Lakes and Northeast.
Especially from about day 5 onward, gradual return of favorable
moisture is likely beneath the southwestern rim of the stronger
associated flow -- from the north-central High Plains to the lower
Missouri and Tennessee Valley regions. This general pattern
conditionally supports some MCS potential, evolving from activity
forming over the Plains and heading southeastward along or just to
the cool side of the sensible baroclinic zone. However, day-to-day
shortwave, low-level boundary and MCV predictability is too low to
assign unconditional probabilities to any given day.

..Edwards.. 08/09/2024

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ACUS48 KWNS 100835
SWOD48
SPC AC 100834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0334 AM CDT Sat Aug 10 2024

Valid 131200Z - 181200Z

...DISCUSSION...
Upper ridging should generally prevail over parts of the Rockies
into the Plains through much of the extended forecast period.
Periodic suppression of the upper ridge should occur as multiple
weak mid-level perturbations move eastward across the
northern/central portions of the CONUS. Isolated strong to severe
thunderstorm potential may exist across parts of the
northern/central Plains into the mid MS Valley and Midwest with any
of these low-amplitude shortwave troughs. For Day 4/Tuesday, the
best severe potential may focus over the northern/central High
Plains along/east of a weak surface trough. However, both
instability and shear appear too limited to include a 15% severe
area. Details on convective evolution become less clear from midweek
onward. But, there are some indications that a shortwave trough may
move across parts of the Plains into the Midwest/mid MS Valley. Even
so, both predictability and forecast strength/amplitude of this
feature remain far too low for any severe probabilities.

..Gleason.. 08/10/2024

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ACUS48 KWNS 110850
SWOD48
SPC AC 110848

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CDT Sun Aug 11 2024

Valid 141200Z - 191200Z

...DISCUSSION...
Multiple mid-level perturbations should move eastward across the northern/central CONUS from the middle of this week through next
weekend. This should generally act to suppress upper ridging to the
southern states through at least Day 5/Thursday. Low predictability
for organized severe potential remains apparent in this flow regime
given the low-amplitude nature of relevant features. But,
medium-range guidance shows a tendency for a more amplified pattern
by late week into the upcoming weekend as an upper trough/low
potentially develops across the western states, ridging builds over
the central CONUS, and a separate upper trough/low remains over the
eastern CONUS. Regardless of these developments, isolated severe
potential may exist on Day 4/Wednesday across parts of the
northern/central Plains and perhaps Upper Midwest in association
with one of the mid-level perturbations. Some threat for organized
severe thunderstorms will probably continue each day through the
extended forecast period across parts of the Plains into the Midwest
and vicinity, although delineating regions of greater potential
remains highly uncertain.

..Gleason.. 08/11/2024

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ACUS48 KWNS 120847
SWOD48
SPC AC 120845

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CDT Mon Aug 12 2024

Valid 151200Z - 201200Z

...DISCUSSION...
Medium-range guidance is in reasonably good agreement that another
weak mid-level shortwave trough will move eastward across the
northern/central Plains to the Upper Midwest on Day 4/Thursday. Some
severe potential may accompany this feature, but forecast deep-layer
shear should tend to remain rather marginal. Differences also exist
in where a greater severe threat may develop across these regions,
so a 15% severe area has not been included. Gradual amplification of
the upper pattern should occur late this week into the upcoming
weekend, with a trough/low developing over the eastern Pacific,
ridging building over much of the western states into the
Rockies/Plains, and troughing over the East. This pattern may
support isolated severe potential each day from Day 5/Friday through
early next week across parts of the central/eastern CONUS, generally along/south of a weak front and in a northwesterly mid-level flow
regime between the upper ridge and eastern states upper trough.
However, predictability of potential MCS corridors and greater
severe potential remain low at this extended time frame.

..Gleason.. 08/12/2024

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ACUS48 KWNS 130845
SWOD48
SPC AC 130844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Tue Aug 13 2024

Valid 161200Z - 211200Z

...DISCUSSION...
Upper ridging over the southern tier of the CONUS should be
suppressed by a slow moving upper trough/low over the Upper Midwest
and Great Lakes on Day 4/Friday. Moderate to locally strong
instability should once again be in place along/ahead of a weak
front. Sufficient mid-level flow and related deep-layer shear should
exist to support at least an isolated severe threat across parts of
the OH Valley/Midwest into the mid MS Valley and southern/central
Plains. However, the presence of prior convection and only weak
low-level convergence along the front lend low confidence in
delineating a corridor of greater severe potential across these
regions Friday afternoon/evening. Have therefore not included a 15%
severe area at this time.

For this weekend into early next week, an upper low should develop
and remain over the eastern Pacific, off the Northwest Coast. Upper
ridging is forecast to build over much of the West and
Rockies/Plains, with upper troughing persisting over the eastern
states. Some severe threat may continue each day across parts of the
Plains into the Southeast and eastern states, along and south/east
of a weak front. But, the overall synoptic pattern suggests limited predictability in highlighting focused areas of greater severe
potential.

..Gleason.. 08/13/2024

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ACUS48 KWNS 140858
SWOD48
SPC AC 140856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Wed Aug 14 2024

Valid 171200Z - 221200Z

...DISCUSSION...
Medium-range guidance remains in good agreement that upper ridging
will remain prominent, and probably further amplify, over much of
the Rockies/Plains this weekend into early next week. An upper
trough should progress slowly eastward from the Midwest/OH Valley to
the eastern states on Day 4/Saturday. While an isolated severe risk
may exist across parts of the Mid-Atlantic into the Southeast ahead
of a weak front, the overall environment currently appears too
marginal given modest deep-layer shear to warrant inclusion of a 15%
severe area for Saturday. Otherwise, an upper trough/low should
mostly remain off the coast of the Pacific Northwest through at
least early next week, before possibly advancing inland towards the
end of the forecast period (around Day 8/Wednesday). There is a fair
amount of uncertainty regarding potential suppression of the upper
ridge early next week. Regardless, the severe threat across the
CONUS may tend to remain fairly isolated in this time frame, with
the exception of potential MCS development from parts of the Plains
into the Midwest/OH Valley in a northwesterly mid-level flow regime.
But, predictability remains far too low to include any areas early
next week.

..Gleason.. 08/14/2024

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ACUS48 KWNS 150858
SWOD48
SPC AC 150856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Thu Aug 15 2024

Valid 181200Z - 231200Z

...DISCUSSION...
As an upper trough moves slowly eastward over the eastern CONUS, an
isolated severe threat may continue on Day 4/Sunday across parts of
the Mid-Atlantic into the Southeast along/ahead of a cold front.
However, the potential stabilizing effects of prior convection,
along with generally modest deep-layer shear, render low confidence
in a more organized severe/damaging wind threat on Sunday. Lower
severe potential is anticipated across the eastern states on Day
5/Monday as the upper trough progresses eastward and the cold front
moves mostly offshore. Upper ridging will likely remain prominent
across much of the Rockies and Plains through at least early next
week, while an upper trough/low generally remains centered off the
coast of the Pacific Northwest. Some chance for severe thunderstorms
may exist over interior portions of the Northwest into parts of the
northern Rockies/Plains and perhaps Upper Midwest next week. But, predictability of various mid-level perturbations that may encourage
robust thunderstorms remains low at this extended time frame.

..Gleason.. 08/15/2024

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ACUS48 KWNS 160845
SWOD48
SPC AC 160844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Fri Aug 16 2024

Valid 191200Z - 241200Z

...DISCUSSION...
...Monday/Day 4 to Wednesday/Day 6...
An upper-level ridge is forecast to remain over the High Plains from
early to mid week, as an upper-level trough moves slowly eastward
across the eastern U.S. Surface high pressure, associated with the
trough is forecast to move from the middle to upper Mississippi
Valley on Monday to the middle and upper Atlantic Seaboard by
Wednesday. Due to this high, the airmass across much of the eastern
third of the U.S. will likely become drier and less unstable from
Monday to Wednesday, making conditions less favorable for severe
storms.

Further to the west, a south-to-north corridor of moderate
instability is forecast to develop each day, remaining in a similar
position across the central and northern Plains. Thunderstorms will
be possible each afternoon and evening to the east of the ridge near
the axis of instability. It appears that deep-layer shear will be
relatively weak near instability axis, which will favor less storm organization. Still, a marginal severe threat will be possible due
to the strong instability.

...Thursday/Day 7 and Friday/Day 8...
The upper-level ridge in the north-central U.S. is forecast to move
eastward from the northern Plains on Thursday into the western Great
Lakes region by Friday. An axis of moderate to strong instability is
forecast to remain over the central and northern Plains.
Thunderstorms that form each afternoon close the instability axis
will have a chance be severe. Although there is a lot of uncertainty
this far out in the forecast cycle, the subsidence and weaker
deep-layer shear associated with the upper-level ridge, should
negatively impact severe potential. However, instability could be
strong enough for a marginal severe threat, mainly during the
afternoon and evening on Thursday and Friday.

..Broyles.. 08/16/2024

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ACUS48 KWNS 170902
SWOD48
SPC AC 170900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Sat Aug 17 2024

Valid 201200Z - 251200Z

...DISCUSSION...
...Tuesday/Day 4 to Thursday/Day 6...
A shortwave ridge over the eastern part of the northern Plains is
forecast to deamplify on Tuesday. Further west, the large-scale
upper-level ridge is forecast to move eastward across the northern
Plains on Tuesday and into the upper Mississippi Valley from
Wednesday into Thursday. This feature will move away from a moist
axis in the northern Plains, where moderate instability is forecast
each afternoon. Thunderstorm development, some with potential for
isolated large hail and severe wind gusts, will be possible each
day. The greatest severe threat during the mid-week is expected on
Wednesday in the Dakotas, where southwest mid-level flow and strong
instability is forecast in the wake of the upper-level ridge.

...Friday/Day 7 and Saturday/Day 8...
On Friday, some model solutions deepen an upper-level trough over
the Intermountain West. In response, the north-central U.S
upper-level ridge would move eastward toward the western Great
Lakes. Isolated thunderstorms, possibly associated with a severe
threat, would be possible within a moist airmass located further to
the west from Nebraska into the Dakotas. However, some solutions are
slow to move the upper-level trough into the western U.S. This would
keep the upper-level ridge further west, negatively impacting the
severe potential across the northern Plains. Under this scenario,
storm coverage would be more isolated and the severe threat would
not be as great.

..Broyles.. 08/17/2024

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ACUS48 KWNS 180851
SWOD48
SPC AC 180850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Sun Aug 18 2024

Valid 211200Z - 261200Z

...DISCUSSION...
...Wednesday/Day 4 to Friday/Day 6...
An upper-level ridge is forecast to gradually deamplify, moving from
the northern Plains on Wednesday to the Great Lakes on Friday. An
axis of instability will likely remain in the central and northern
Plains from mid to late week, where isolated to scattered
thunderstorms are expected to develop each afternoon and evening.
The strongest instability is forecast over the Dakotas on Wednesday,
with the ECMWF having SBCAPE peak above 4000 J/kg along the
instability axis. This, combined with 0-6 km shear in the 30 to 40
knot range, would support isolated supercell development. Large hail
and severe wind gusts would be the primary threats. However, some
solutions suggest that the upper-level ridge will be slower to move
eastward, which would keep convection more isolated on Wednesday.
For this reason, will not add a threat area for Wednesday. A similar
setup is forecast on Thursday and Friday, which would support a
marginal severe threat across the northern Plains each afternoon and
evening.

...Saturday/Day 7 and Sunday/Day 8...
On Saturday, some of the medium-range models have an upper-level
trough moving through the northern Rockies and Intermountain West. Southwesterly flow would be in place across much of the
north-central U.S. Ahead of this feature, scattered thunderstorm
would be possible across parts of the northern High Plains and
Dakotas. Under this scenario, which is favored by the ECMWF, severe
storms would be possible in parts of the northern Plains extending south-southeastward along the instability axis into the mid Missouri
Valley. The severe threat would be shifted eastward into the parts
of the upper Mississippi Valley on Sunday. For the weekend, other
models are considerably slower with the progression of the western
U.S. upper-level trough, which adds a lot of forecast uncertainty.

..Broyles.. 08/18/2024

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ACUS48 KWNS 190853
SWOD48
SPC AC 190851

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0351 AM CDT Mon Aug 19 2024

Valid 221200Z - 271200Z

...DISCUSSION...
...Thursday/Day 4 to Saturday/Day 6...
An upper-level ridge is forecast to gradually build over the Great
Plains from Thursday to Saturday. During this time period, an axis
of low-level moisture and instability is forecast to remain over the
central and northern Plains. As surface temperatures warm each day,
isolated thunderstorms are expected to develop over parts of the
moist airmass. Moderate deep-layer shear and steep lapse rates
should be favorable for a severe threat, with large hail and severe
wind gusts possible. However, large-scale ascent and the resultant
convective coverage is forecast to be limited, which should reduce
the overall severe threat coverage.

...Sunday/Day7 and Monday/Day 8...
An upper-level low over the Desert Southwest is forecast by the
ECMWF to move quickly northeastward across the Intermountain West on
Sunday, and into the northern Plains on Monday. Ahead of this
feature, the medium range models suggest that a broad corridor of
strong instability will be in place. Although convective coverage
may remain relatively isolated on Sunday and Monday, the strong
instability should be favorable for a severe threat. Large hail and
isolated severe wind gusts would be possible in the northern Plains
on Sunday, and in the upper Mississippi Valley on Monday. However,
there is a wide dispersion of solutions concerning the timing of the upper-level trough. This suggest that uncertainty is substantial
from Sunday into Monday. Once the models become in better agreement,
a threat area may need to be considered early next week if it
appears that convective coverage over the warm sector will be
sufficient.

..Broyles.. 08/19/2024

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ACUS48 KWNS 200839
SWOD48
SPC AC 200838

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0338 AM CDT Tue Aug 20 2024

Valid 231200Z - 281200Z

...DISCUSSION...
...Friday/Day 4 to Sunday/Day 6...
Heights within the persistent central U.S. upper-level ridge are
forecast to rise from Friday to Sunday, as a mid-level trough moves
through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern
Plains extending south-southeastward into the mid Missouri Valley.
Thunderstorm development, with a potential severe threat, will be
possible across parts of this unstable airmass each afternoon and
evening. Subsidence associated with the upper-level ridge will be a
negative factor, which is expected to keep the severe threat
isolated and marginal through the weekend.

...Monday/Day 7 and Tuesday/Day 8...
The medium-range models are finally in agreement concerning the
timing of an upper-level trough, which is forecast to move through
the northern Plains on Monday. Ahead of this trough, a moist and
unstable airmass is forecast from the mid Missouri Valley
northeastward into the western Great Lakes. Thunderstorms are
expected to develop ahead of the trough over parts of the Minnesota
and Wisconsin, with more isolated convection southward into Iowa.
Strong instability and moderate deep-layer shear should be favorable
for a severe threat, with the most likely area in the upper
Mississippi Valley Monday afternoon and evening. However, there is
still uncertainty concerning the timing of the trough, and location
of the instability axis on Monday. In addition, part of the airmass
could remain capped. At this point, will not outlook a threat area.
The potential severe threat is forecast to shift eastward into the
central Great Lakes region on Tuesday, but could be isolated due to
the presence of a northeastern U.S. upper-level ridge.

..Broyles.. 08/20/2024

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ACUS48 KWNS 210856
SWOD48
SPC AC 210855

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CDT Wed Aug 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
...Saturday/Day 4 to Monday/Day 6...
Heights within an upper-level ridge are forecast to rise across the
central and northern U.S over the weekend, as an upper-level trough
moves across the western U.S. Isolated severe-thunderstorm
development will be possible across the Dakotas in the afternoon and
evening both Saturday and Sunday. The best chance for severe storms
would be on Sunday as large-scale ascent and deep-layer shear both
increase across the northern Plains due to the approach of the
trough.

The severe threat is forecast to shift eastward into the upper
Mississippi Valley on Monday, as the upper-level trough and its
associated cold front advance eastward from the northern Plains into
the upper Mississippi Valley.

...Tuesday/Day 7 and Wednesday/Day 8...
On Tuesday and Wednesday, the upper-level trough is forecast to
deamplify as it moves through the Great Lakes region. Another
upper-level trough is forecast to move through the western U.S on
Tuesday and Wednesday. The best chance for severe storm development
would be on Wednesday afternoon along an instability axis, most
likely in either eastern parts of the northern Plains or in the
upper Mississippi Valley. At this range, large model spread
concerning the timing of the trough and distribution of instability
suggests uncertainty is substantial.

..Broyles.. 08/21/2024

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ACUS48 KWNS 220901
SWOD48
SPC AC 220900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Thu Aug 22 2024

Valid 251200Z - 301200Z

...DISCUSSION...
...Sunday/Day 4 to Tuesday/Day 6...
Heights within an upper-level ridge over the Mississippi Valley will
continue to rise on Sunday, as an upper-level trough moves through
the western U.S. The ridge is forecast to move into the western
Great Lakes from Monday into Tuesday, as the upper-level trough
moves across the north-central U.S. Ahead of the approaching trough, thunderstorm development will be possible each day, from the
northern Plains into the upper Mississippi Valley. For the three
days, the greatest chance of severe storms appears to be in the
Dakotas on Sunday and in the upper Mississippi Valley on Monday.
Strong instability and moderate deep-layer shear, combined with
increasing large-scale ascent, should result in a severe threat each
afternoon and evening. Large hail and severe gusts will likely be
the primary threats.

...Wednesday/Day 7 and Thursday/Day 8...
On Wednesday and Thursday, the upper-level trough is forecast to
move across the upper Mississippi Valley and into southern Canada,
as a second trough moves through the northern Plains. At the
surface, a moist airmass is forecast to remain in place over the
Great Lakes region and Upper Midwest. Scattered to widely scattered thunderstorms will be possible across much of this moist airmass on
both days. Although an isolated severe threat will be possible each
afternoon and evening, the threat is expected to remain marginal due
to a large area of mid-level high pressure that is forecast to be in
place over much of the eastern half of the nation.

..Broyles.. 08/22/2024

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ACUS48 KWNS 230902
SWOD48
SPC AC 230901

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0401 AM CDT Fri Aug 23 2024

Valid 261200Z - 311200Z

...DISCUSSION...
Models continue to suggest potential for severe weather across parts
of the Upper Mississippi Valley area Day4/Monday, as a mid-level
short-wave trough is shunted northeastward across this region by the
persistent central U.S. ridge. Timing of the advance of this
feature differs between the GFS and ECMWF, casting some uncertainty,
but enough agreement exists to maintain a 15% probability area
across this region.

One other area of interest Day 4/Monday is across portions of the
southern New England/Mid-Atlantic vicinity within a northwesterly
flow regime on the southwestern side of New England/Canadian
Maritimes upper low. Enhanced northwesterlies aloft would be
sufficient to produce rather fast-moving bands of storms, but degree
of instability remains a substantial question at this time. With
intensity of the convection thus still uncertain, will refrain at
this time from introducing a risk area.

As the north-central U.S. mid-level feature moves into/across
Ontario Day 5, a decrease in severe risk is expected despite a weak
frontal advance southeastward across the Great Lakes into the Ohio
Valley.

Beyond Day 5, models begin to deviate substantially, particularly
with respect to their handling of the next trough expected to
progress eastward across the Canadian Prairie and
northwestern/north-central CONUS. While some severe potential could
accompany this feature, particularly if an evolution that resembles
the stronger ECMWF solution plays out, uncertainty precludes any
reasonable assessment of severe potential.

..Goss.. 08/23/2024

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ACUS48 KWNS 240855
SWOD48
SPC AC 240854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Sat Aug 24 2024

Valid 271200Z - 011200Z

...DISCUSSION...
Within the faster belt of upper flow across the northern U.S.,
substantial differences in timing of the disturbances in the flow
are manifest from the very start of the medium-range period. On
Tuesday/Day 4, an energetic short-wave trough should be crossing the north-central U.S., headed toward the Upper Mississippi
Valley/southern Ontario, while an upstream trough crosses western
Canada and the Pacific Northwest, and a downstream one crosses
northern Quebec. However, noted differences in both timing and
orientation of these features is immediately apparent. The
north-central U.S. feature -- the one associated with Day-4 severe
risk over the Great Lakes region -- is roughly 12 hours slower, and
evolves to a more negatively tilted configuration in the ECMWF, as
compared to the GFS. This results in fairly substantial differences
in the surface pattern as well, prohibiting any forecast of the
specifics regarding the severe-weather potential on Tuesday. Still, severe-weather risk is apparent despite east-west geographical
uncertainties. Thus, will introduce an elongated 15% area across
the Upper Midwest and Great Lakes region, given likelihood for
existence of a favorably unstable/amply sheared environment in the
vicinity of a surface front likely to stretch east-northeastward to west-southwestward across this region. Damaging winds and hail
would likely be the primary risks.

By Day 5, differences continue to amplify. Risk for severe weather
may evolve across portions of the Northeast (favored by the GFS),
and/or parts of the Midwest/Ohio Valley (favored by the ECMWF).
However, the differences are substantial enough amongst the models
to preclude an areal highlight at this time. Meanwhile farther
west, an upper low/trough is forecast to be moving across the
northwestern U.S. and Canadian Prairie early in the day, but
location/timing, and intensity differences with this feature are
pronounced. While some severe risk may evolve across parts of the north-central U.S. ahead of this feature and an associated cold
front, the differences preclude any areal outlines at this time.

Predictability issues persist through the remainder of the period,
with model solutions diverging steadily through the upcoming Labor
Day weekend.

..Goss.. 08/24/2024

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ACUS48 KWNS 250900
SWOD48
SPC AC 250859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Sun Aug 25 2024

Valid 281200Z - 021200Z

...DISCUSSION...
Potential for severe weather may spread across parts of the
Northeast/New England Day 4/Wednesday. However non-trivial
uncertainty is evident -- regarding both details with respect to how
the short-wave trough crossing Ontario interacts with the more
pronounced trough shifting eastward across Quebec into the Canadian
Maritimes, as well as evolution/progression of ongoing Day-3
convection. Therefore, despite potential for severe weather that is
evident in a broad/general sense, no areas will be highlighted at
this time.

Upstream, models forecast the advance of an upper low across the
Canadian Prairie, with troughing south of the low to cross the
northern Intermountain Region and eventually reach the northern
Plains. As this system advances, a cold front is progged to move
into/across the Dakotas and western Nebraska diurnally. Amply
strong flow should accompany this trough, along with the likelihood
for sufficient warm-sector destabilization to support storm
development. This suggests some potential for severe weather across
portions of the northern Plains, but -- similar to the potential for
severe weather over the Northeast -- will refrain from any areal
highlights at this time.

Beyond Day 4/Wednesday, model differences steadily increase with
respect to the large-scale features, and thus will refrain from
attempts to assess risk through the remainder of the medium-range
period.

..Goss.. 08/25/2024

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ACUS48 KWNS 260845
SWOD48
SPC AC 260844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Mon Aug 26 2024

Valid 291200Z - 031200Z

...DISCUSSION...
An upper low is forecast to move across the Canadian Prairie and
north-central U.S. through the first half of the Day 4/Thursday
period, before being shunted a bit northeastward into Ontario due to
pronounced downstream ridging. Timing differences amongst the
medium-range global models with the advance of this feature,
similarly result in positional differences with the surface front.
Thus, while some severe risk may manifest during the
afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment
ahead of the front, no risk areas will be highlighted at this time.

Similarly on Day 5/Friday, timing differences are evident as upper
troughing and the associated surface front shift across the Upper
Great Lakes/Midwest region. While some severe risk would again be
possible within this general region, too much positional uncertainty
exists for areal outlines.

Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast
across roughly the eastern half of the country -- though to
different degrees in the various models. As this occurs, the more
favorably moist low-level airmass will gradually be suppressed
southward, south of the faster belt of flow aloft, and thus a
general decrease in severe risk is expected across the U.S. overall.
This trend should continue through the end of the period, as a
pronounced intrusion of Canadian air gradually spreads across the
eastern two-thirds of the country through Labor Day and beyond.

..Goss.. 08/26/2024

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ACUS48 KWNS 270904
SWOD48
SPC AC 270902

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0402 AM CDT Tue Aug 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
Latest runs of the global models suggest that the general pattern
evolution over the U.S. through the medium range will be
characterized by a slowly progressive upper flow field, trending
toward amplification of troughing over the eastern U.S. and ridging
over the West. Late in the period, as the pattern continues to
progress, a Pacific trough is progged to approach and then move into
the western states, while the western U.S. ridge shifts gradually
toward the central states. Still farther upstream, the eastern U.S.
trough will likewise continue shifting eastward, into/across New
England and the Canadian Maritimes.

Through the first half of the period, as the upper trough moves
across the Great Lakes region and adjacent Ontario and is then
reinforced by a second feature digging southeastward out of Canada,
a series of surface cold fronts will shift eastward/southeastward
across the central and eastern CONUS.

On Day 4/Friday, at least some severe threat will likely evolve over
the Upper Great Lakes/Midwest, ahead of the initial cold front. By
Day 5/Saturday, convection -- and possibly limited severe risk --
may spread across the Lower Lakes and Ohio Valley area. A
continued, eastward shift should persist through Day6/Sunday, as the
next front accelerates eastward across the Great Lakes/Midwest, with
most substantial strong convective potential evolving from New
England into the Mid-Atlantic region. Overall however, with
low-level moisture begin suppressed gradually southward by Canadian
frontal intrusions, and the surface baroclinic zone settling south
of the stronger flow aloft, overall risk should remain limited, and
gradually decreasing through the period. As such, no risk areas are
being included in the medium-range outlook at this time.

..Goss.. 08/27/2024

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ACUS48 KWNS 280857
SWOD48
SPC AC 280856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Wed Aug 28 2024

Valid 311200Z - 051200Z

...DISCUSSION...
Medium-range global models continue to suggest limited severe
potential Days 4-5 (Saturday and Sunday) largely within the
northeastern quarter of the country, followed by several days of
what appears likely to be minimal severe risk through the remainder
of the period.

Day 4/Saturday, upper-level height falls are progged to shift across
the Great Lakes/Midwest/Northeast, as a strengthening upper trough
advances east-southeastward across Ontario and the Upper Great Lakes
region. A weak cold front will cross the Lower Great
Lakes/Appalachians, with likelihood for showers and thunderstorms
accompanying this front. However, with stronger flow aloft limited
to areas from Pennsylvania northward, where instability should
remain limited, overall severe risk appears at this time to remain
too low to warrant inclusion of a risk area associated with this
frontal passage.

Limited severe potential may also exist for a few hours in the
afternoon and early evening over the Upper Mississippi Valley area,
as a stronger/reinforcing cold front surges southeastward out of
Canada across the Upper Mississippi Valley and Great Lakes region
and into central Plains and Upper Midwest overnight. Though only
modest moisture -- and thus weak afternoon pre-frontal
destabilization -- is expected, low-topped convection is expected
during the afternoon across parts of Upper Michigan/Wisconsin and
perhaps Minnesota. Strong northwesterly flow aloft would support
fast-moving storms, and possibly a risk for damaging winds locally.
Again though, this potential appears too limited/uncertain to
include a risk area at this time.

Day 5, the surging cold front is forecast to shift southeastward
into the Northeast/New England, and southward across the Ohio Valley
area. Similar to Day 4 potential for low-topped storms farther
northwest, convection will likely develop along the front through
the afternoon -- particularly across the New England vicinity.
However, given the frontal passage the prior day, questions with
respect to available moisture -- and thus destabilization potential
-- exist at this time. As such, despite the strong front and strong
flow aloft, severe risk again appears limited and uncertain,
precluding introduction of a risk area for now.

The cold front is expected to have moved offshore of New England and
the Mid-Atlantic region by the start of Day 6, becoming
quasistationary in a west-to-east manner across the Southeast and
Mid South, on the southern fringe of a Canadian High settling into
the northeastern quarter of the country. While convection will
likely occur near and south of this front where moist Gulf air will
remain in place, this region will remain well south of the enhanced
flow aloft. Therefore, severe risk appears minimal -- and should
remain so through the end of the period.

..Goss.. 08/28/2024

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ACUS48 KWNS 290902
SWOD48
SPC AC 290900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Thu Aug 29 2024

Valid 011200Z - 061200Z

...DISCUSSION...
Medium-range/global models are in reasonably good agreement with
respect to synoptic-scale features across the U.S. through about Day
6/Tuesday. Late in the period, models begin deviating with respect
to their handling of an upper low, which through the first half of
the period is progged to be moving in a slow, anticyclonic arc
around northern fringes of a western and central U.S. ridge. As
this feature crests the ridge, moving across the northern
Intermountain region Day 7/Wednesday, model solutions begin to
diverge with respect to progression of the system, with divergence
continuing through Day8. Therefore, while some severe risk may
accompany the advance of this feature toward/into the north-central
U.S. late in the period, uncertainty precludes any further
assessment of this potential.

Meanwhile early in the period, an upper trough will shift across the northeastern quarter of the country Day 4/Sunday. An associated
cold front is progged to advance across the Northeast/Mid-Atlantic
region, but with preceding low-level moisture likely already swept
off the New England Coast by a prior frontal passage. As such, it
appears that only a limited potential for stronger storms will exist
along trailing portions of the front farther south (from the
Mid-Atlantic vicinity westward into the Tennessee Valley area) with
stronger flow aloft remaining farther to the north.

Days 5-6 and beyond, the front will continue sagging southward
across the Southeast and Gulf Coast States, as a Canadian surface
high settles southeastward into the Plains/Great Lakes/Midwest.
While convection can be expected near and south of this boundary,
stronger flow aloft will remain well north of this region, thus
precluding organized severe potential.

..Goss.. 08/29/2024

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ACUS48 KWNS 300837
SWOD48
SPC AC 300835

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0335 AM CDT Fri Aug 30 2024

Valid 021200Z - 071200Z

...DISCUSSION...
Global models appear to be in reasonable agreement through the
medium range, with a long-wave upper trough crossing the eastern
U.S. Day 4/Monday, and then shifting into the Canadian Maritimes and
western Atlantic Day 5/Tuesday. Weak/low-amplitude flow aloft will
prevail across the U.S. Day 5 and into Day 6/Wednesday, before the
pattern begins to amplify again through Days 7-8 (Thursday and
Friday, Sept. 5-6). This amplification anticipated late in the
period will result in an eastern trough/western ridge configuration,
with a cold front to progress across the eastern half of the country
through the second half of the period.

However, with the prior (Day 3) frontal advance across the southern
U.S., and persistence of Canadian surface high pressure in its wake,
rich/Gulf moisture is expected to remain confined to southern
portions of the country. This should limit severe potential with
the late-period system as it crosses the CONUS. As such, no
severe-weather risk areas are being included in the forecast, as
overall potential appears likely at this time to remain low through
the end of the upcoming week.

..Goss.. 08/30/2024

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ACUS48 KWNS 310834
SWOD48
SPC AC 310833

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CDT Sat Aug 31 2024

Valid 031200Z - 081200Z

...DISCUSSION...
Global models are in reasonable agreement with handling of
large-scale features through about Day 5/Wednesday, after which
divergent tendencies become apparent -- particularly with the
handling of a weak short-wave feature moving across the northwestern
U.S. early in the period. Models depict this feature partially
phasing with a more substantial trough moving across western Canada
within the faster belt of westerlies to the north Day 4/Tuesday, and
then emerging into the north-central U.S. Day 5. Afterward,
evolution of this trough begins to differ substantially amongst the
models. The GFS depicts this trough evolving into cut-off low over
the Upper Mississippi Valley/Upper Great Lakes region Day
6/Thursday, which then lingers in place through Day 8 and beyond.
Meanwhile, the ECMWF remains slowly progressive with the trough into
eastern North America through the period. Given these substantial
differences, convective/severe potential cannot be reasonably
assessed beyond Day 5.

In the Day 4-5 time frame, a cold-frontal advance out of the western
U.S. into the northern Plains -- and eventually the Great Lakes
region -- is expected, in tandem with the progression of the
aforementioned upper trough. However, with a surface high still
firmly in place from the eastern U.S. westward into the
central/southern Plains, Gulf moisture will remain suppressed, and
thus the likelihood for only meager destabilization across the
pre-frontal warm sector. Therefore, severe risk is expected to
remain limited, thus not requiring a 15% areal outline associated
with this system through Day 5.

..Goss.. 08/31/2024

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ACUS48 KWNS 010850
SWOD48
SPC AC 010849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sun Sep 01 2024

Valid 041200Z - 091200Z

...DISCUSSION...
Similar to 24 hours prior, global model solutions with respect to
the large-scale pattern evolution over the U.S. begin substantial
divergence relatively early in the medium-range period. This
deviation in solutions becomes readily apparent by Friday (Day 6),
and the differences preclude any meaningful assessment of severe
risk beyond Thursday (Day 5).

Through Day 5, severe-weather risk appears likely to remain minimal.
Though a cold front is forecast to cross the northern Plains
Wednesday (Day 4) and the Upper Mississippi Valley/Upper Great Lakes
region Thursday (Day 5), low-level moisture -- and thus potential
for destabilization -- is forecast to remain limited ahead of the
front. As such, appreciable severe risk appears unlikely at this
time.

..Goss.. 09/01/2024

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ACUS48 KWNS 020901
SWOD48
SPC AC 020900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Mon Sep 02 2024

Valid 051200Z - 101200Z

...DISCUSSION...
Global models have come into a bit better agreement with each other,
through late next week, with respect to their handling of the
large-scale features. Day 4 (Thursday), the upper trough crossing
central portions of Canada and the north-central U.S. is progged to
continue digging southeastward -- reaching a roughly upper
Mississippi Valley to Mid-Missouri Valley position by Friday
morning. As this occurs, a corresponding eastward/southward advance
of a surface cold front will occur, crossing the Upper Great
Lakes/Upper Midwest and drifting as far south as the central Plains
overnight. Preceding the front, limited low-level moisture is
expected, with Gulf moisture remaining restricted to the
southern-tier states. Thus, while a few strong/severe storms may
evolve within a southern Upper Great Lakes to central Plains
corridor, potential for a more widespread severe event appears
limited at this time.

Day 5 (Friday), a continued southeastward advance/amplification of
the upper trough is anticipated, shifting across the Great Lakes and
Midwest through the day, and with cyclonic flow surrounding the
trough to encompass the entire eastern half of the country by
Saturday morning. The associated cold front -- crossing the central
U.S. through the day, is expected to reach a Lower Great Lakes to
Lower Mississippi Valley to Texas position overnight. Meanwhile,
the height falls associated with this trough into the southeastern
U.S. may support frontal wave development along the remnant
baroclinic zone likely to be lingering over the northern Gulf/Gulf
Coast area. While still uncertain, this low may shift across the
Southeast Friday, reaching the eastern Carolinas vicinity by Sunday
morning. While it is not out of the question that -- with this
front/low marking the northward extent of tropical low-level air,
that low-end severe risk could evolve overnight. However, this
scenario is uncertain, and would seem likely to remain limited in
terms of significance.

Day 6, some negative tilt of the upper trough is expected as it
advances across the Midwest and Lower Great Lakes area, with models
suggesting evolution into a closed low over the eastern Ontario
vicinity with time. Meanwhile, the advancing cold front is progged
to begin to overtake the remnant baroclinic zone and frontal wave,
with the combined front to linger near -- and eventually move off --
the Atlantic Seaboard as the frontal low moves toward/into southern
New England overnight. Again, some severe potential may manifest
ahead of the consolidating surface front, but at this time, models
suggest that destabilization will remain largely just offshore.

By Sunday (Day 7) and continuing through the end of the period,
model divergence increases -- with evolution/positioning of the
deepening closed low over eastern NOAM, and -- as a result, the
upstream flow pattern over the western half of the country. Overall
severe risk would appear to be low overall however, with general
ridging likely over the western half of the country.

..Goss.. 09/02/2024

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ACUS48 KWNS 030824
SWOD48
SPC AC 030823

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0323 AM CDT Tue Sep 03 2024

Valid 061200Z - 111200Z

...DISCUSSION...
On D4/Friday, on upper-level trough is forecast to amplify as it
digs southeastward across the Great Lakes region. In response, a
surface low is forecast to deepen in the vicinity of the lower Great
Lakes, though the timing and intensity of cyclogenesis continues to
vary among extended-range guidance. Depending on the timing of the
upper-level trough and attendant cold front, strong storms could
develop across parts of the Ohio Valley during the afternoon and
evening as low/midlevel flow strengthens, though generally weak
instability could tend to limit severe potential.

Uncertainty regarding the synoptic evolution on D4/Friday continues
into D5/Saturday. However, there will be some potential for
low-level moisture to be drawn northward into parts of the Mid
Atlantic and Northeast, in advance of the cold front. Instability
may remain quite weak, but rather strong flow could support
convection with gusty-wind potential, if adequate prefrontal
buoyancy can develop.

For D6/Sunday and beyond, most guidance keeps richer low-level
moisture confined near the Gulf Coast, which could generally limit
severe potential across much of the CONUS. One possible exception is
the High Plains vicinity, where modest low-level moisture return
could support some increase in convective potential, especially if a northwesterly flow regime can be maintained between the deep eastern
trough and an upper ridge that may become reestablished near the
Four Corners region. However, predictability regarding synoptic
details begins to substantially wane into early next week.

..Dean.. 09/03/2024

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ACUS48 KWNS 040811
SWOD48
SPC AC 040810

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0310 AM CDT Wed Sep 04 2024

Valid 071200Z - 121200Z

...DISCUSSION...
...D4/Saturday - D5/Sunday: Northeast/Mid Atlantic...
An amplifying trough is forecast to evolve into a rather deep
mid/upper-level cyclone over parts of Ontario into the eastern Great
Lakes region on Saturday, and then begin moving eastward on Sunday.
Uncertainty remains regarding the intensity/location of related
surface cyclogenesis, and the timing of an attendant cold front into
parts of the Northeast and Mid Atlantic. There will be some
potential for low-level moisture to be drawn northward in advance of
the cold front, though instability will likely remain weak. If
adequate buoyancy can develop, then increasing flow fields could
support some increase in severe potential across parts of the Mid
Atlantic and Northeast on D4/Saturday. Uncertainty regarding frontal
position increases into D5/Sunday, though some guidance suggests
potential for frontal convection to develop across parts of New
England before moving offshore.

...D6/Monday - D8/Wednesday...
The deep trough over the eastern CONUS is generally forecast to
weaken and move offshore early next week. Farther west, an upper
ridge is forecast to amplify over the Southwest, while an upper
trough deepens over the eastern Pacific and eventually begins to
impinge upon the Pacific Coast. A persistent surface ridge over the
East is expected to keep richer low-level moisture confined to near
the Gulf Coast, which will tend to limit moisture return and severe-thunderstorm potential across much of the CONUS.

..Dean.. 09/04/2024

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ACUS48 KWNS 050815
SWOD48
SPC AC 050813

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0313 AM CDT Thu Sep 05 2024

Valid 081200Z - 131200Z

...DISCUSSION...
A deep upper-level trough initially over the eastern CONUS on
D4/Sunday is forecast to move offshore early next week. In the wake
of this trough and its attendant cold front, a surface ridge is
expected to persist over much of the eastern CONUS through mid week.
This ridge will likely prevent the northward return of richer
low-level moisture for most of the extended-range period, which
should tend to limit organized severe-thunderstorm potential across
much of the CONUS.

There is some potential for the influence of the eastern surface
ridge to wane by D7/Wednesday into D8/Thursday, while some guidance
suggests a mid/upper-level trough will approach the central/northern
High Plains during this time frame. Should this occur, there could
be some increase in severe potential, though predictability remains
rather low at this forecast range.

..Dean.. 09/05/2024

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ACUS48 KWNS 060853
SWOD48
SPC AC 060852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Fri Sep 06 2024

Valid 091200Z - 141200Z

...DISCUSSION...
...Monday/Day 4 to Wednesday/Day 6...
An upper-level trough is forecast to move from the Northeast into
the Atlantic early in the week, as a shortwave ridge moves through
the Great Lakes. Another shortwave trough is forecast to move
through the north-central U.S. At the surface, a large area of high
pressure is forecast to remain over the eastern third of the U.S.
This will likely impede moisture return over the southern U.S.
through midweek. While thunderstorms will be possible near the Gulf
Coast each day, deep-layer shear is forecast to be too weak for
severe storms. Isolated thunderstorms may also develop each
afternoon in parts of the north-central states, but limited
large-scale ascent and relatively weak deep-layer shear should be
unfavorable for organized storms.

...Thursday/Day 7 and Friday/Day 8...
Low-level moisture is forecast to return northward into the Arklatex
on Thursday, as a shortwave trough moves through the south-central
U.S. Thunderstorm development, with some potentially severe, will be
possible within the moist airmass from the southern Plains eastward
into the lower to mid Mississippi Valley. There is considerable
uncertainty concerning the timing of the shortwave trough and
instability. For this reason, the area with the greatest threat is
unclear at this time. On Friday, moisture advection is forecast to
continue across the central U.S. as the western U.S. upper-level
trough approaches the central and northern Plains. Isolated severe thunderstorms will be possible ahead of the trough in the
north-central states. Uncertainty on Friday is again substantial due
to the relatively wide dispersion among the model solutions.

..Broyles.. 09/06/2024

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ACUS48 KWNS 070854
SWOD48
SPC AC 070853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0353 AM CDT Sat Sep 07 2024

Valid 101200Z - 151200Z

...DISCUSSION...
...Tuesday/Day 4 to Thursday/Day 6...
A shortwave ridge is forecast to move eastward across the Great
Lakes region on Tuesday and into the Northeast on Wednesday. Another
shortwave ridge is forecast to move through the north-central U.S.
on Wednesday as an upper-level trough amplifies across the western
U.S. Due to the presence of instability in the northern Plains,
thunderstorm development will be possible each afternoon. However,
large-scale ascent is expected to be limited and deep-layer shear
relatively weak, suggesting that storms should remain isolated and
unorganized. Additional storms will be possible near the Gulf Coast
each day.

...Friday/Day 7 and Saturday/Day 8...
The western U.S. upper-level trough is forecast to move through the
Rockies and into the north-central states from Friday into Saturday.
As the trough moves out, large-scale ascent is forecast to
overspread a moist and unstable airmass in the northern and central
Plains. Although some severe threat will be possible ahead of the
trough, deep-layer shear is forecast to be relatively weak. This
suggests that any severe threat that develops during the afternoon
and evening should remain isolated.

..Broyles.. 09/07/2024

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ACUS48 KWNS 080852
SWOD48
SPC AC 080850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Sun Sep 08 2024

Valid 111200Z - 161200Z

...DISCUSSION...
...Wednesday/Day 4 to Friday/Day 6...
An upper-level ridge is forecast to move across the north-central
U.S. on Wednesday, as a trough develops in the western U.S. An
upper-level low is forecast to move across the northwestern states
from Wednesday to Friday. Ahead of the trough, thunderstorms will be
possible each day from the Intermountain west eastward into the
central and northern Plains. At this time, the potential for severe
may be limited by instability, which is generally forecast to remain
weak across most of the western and central U.S.

In the Gulf Coast region, some model forecasts have a tropical
system becoming organized in the northern Gulf from Wednesday to
Friday. If this system materializes and can move onshore, the day
with the greatest potential to impact the central Gulf Coast would
be Thursday. A tornado threat could materialize as the system moves
inland, depending upon its overall strength.

...Saturday/Day 7 and Sunday/Day 8...
A shortwave trough is forecast to move eastward across the
north-central U.S. on Saturday, as an upper-level low moves across
the Ohio Valley and into the Great Lakes from Saturday into Sunday.
Although the potential for severe storms over the weekend appears to
be low at this time, substantial uncertainty exists at this extended
range.

..Broyles.. 09/08/2024

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ACUS48 KWNS 090852
SWOD48
SPC AC 090851

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0351 AM CDT Mon Sep 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
...Thursday/Day 4 to Saturday/Day 6...
A tropical cyclone is forecast to move slowly northward through the
lower to mid Mississippi Valley from Thursday to Saturday. A tornado
threat will be possible to the east of the center across much of the
central Gulf Coast region on Thursday. Model forecasts suggest that
the tornado threat could shift northward into the Tennessee Valley
on Friday. On Saturday, uncertainty is considerable concerning the
location of any tropical cyclone remnants. If current solutions are
reasonably close, then a tornado threat would be possible in the
Southeast, potentially from the southern Appalachians into the
Carolinas.

...Sunday/Day 7 and Monday/Day 8...
Mid-level flow is forecast to be relatively weak across the central
and eastern U.S. on Sunday and Monday. The diffuse pattern and weak
deep-layer shear across most of the U.S. suggests that the severe
potential will remain low.

..Broyles.. 09/09/2024

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ACUS48 KWNS 100836
SWOD48
SPC AC 100834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0334 AM CDT Tue Sep 10 2024

Valid 131200Z - 181200Z

...DISCUSSION...
Severe potential appears low through the period. Primary concern for
D4/Friday is any lingering tornado threat associated with the
remnants of TC Francine. It is forecast by NHC to drift into the
Mid-South/MS Valley to Lower OH Valley vicinity. Latest guidance
indicates further weakening of low-level wind fields on Friday,
likely becoming inadequate to sustain a synoptically evident TC
tornado threat.

Beyond this time frame, a quiescent pattern for severe is expected
this weekend into early next week. Towards mid-week, majority of
ensemble guidance suggests potential large-scale amplification of an
upper trough into the West. This may yield an increase of
low-probability severe around D8 and beyond over parts of the Great
Plains, where many preceding days of above-normal temps will occur.

..Grams.. 09/10/2024

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ACUS48 KWNS 110845
SWOD48
SPC AC 110844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Wed Sep 11 2024

Valid 141200Z - 191200Z

...DISCUSSION...
Severe potential appears low during much of the period, with an area
of interest on D7/Tuesday in the northern Great Plains vicinity.
Guidance consensus suggests a large-scale trough should approach the
West Coast by about D5/Sunday. An embedded shortwave impulse is
generally projected to move northeast across the central Rockies
into the northern High Plains early next week. This may yield at
least a low-probability severe threat, seemingly centered on
D7/Tuesday, in parts of the Dakotas to eastern MT. Typical spread
for this time frame and only modest run-to-run continuity suggest predictability is too low for a 15 percent severe area.

..Grams.. 09/11/2024

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ACUS48 KWNS 120830
SWOD48
SPC AC 120829

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0329 AM CDT Thu Sep 12 2024

Valid 151200Z - 201200Z

...DISCUSSION...
Severe potential appears low during much of the period, but a
low-probability threat may evolve around D6/Tuesday in the
northern/central High/Great Plains vicinity. With weak flow and a
blocking pattern in the East, a large-scale trough should reach the
West Coast by D4/Sunday. Guidance consensus continues to indicate an
embedded shortwave trough ejecting east-northeast over parts of the
West, before pivoting more north-northeastward towards mid-week.
However, run-to-run oscillation persists with both its spatial
evolution and amplitude of an attendant mid-level jet. Today's 00Z
runs suggest a more marginal setup for a 15 percent highlight.

..Grams.. 09/12/2024

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ACUS48 KWNS 130843
SWOD48
SPC AC 130841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Fri Sep 13 2024

Valid 161200Z - 211200Z

...DISCUSSION...
Guidance has trended increasingly consistent with the evolution of a
closed mid/upper low initially over northern/central CA at 12Z
Monday. This low should become an open wave as it pivots northeast
towards the northern High Plains by late Tuesday, likely inducing
surface cyclogenesis in the eastern MT vicinity. Despite increasing
agreement in track/timing, the consensus trend is for a weakening
mid-level jet ejection, in the meridional flow regime ahead of the
trough. As such, the amplitude of the severe-storm risk is still
uncertain, but an area of interest for a future 15 percent highlight
remains evident across the northern High Plains.

This shortwave trough should dampen and slow as it encroaches on the
persistent blocking pattern in the East. In the wake of this wave,
the next in a series of shortwave impulses should amplify along the
Pacific Coast mid-week. Thereafter, predictability drops
considerably by late week.

..Grams.. 09/13/2024

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ACUS48 KWNS 140844
SWOD48
SPC AC 140842

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0342 AM CDT Sat Sep 14 2024

Valid 171200Z - 221200Z

...DISCUSSION...
...D4...
Severe potential may be maximized on D4/Tuesday, but persistent
predictability concerns preclude a 15 percent highlight.

A mid-level low centered the ID/NV/UT border area at 12Z Tuesday
should advance north-northeast towards the MT/AB/SK border area by
12Z Wednesday. Guidance has improved consistency with this track.
But models remain inconsistent with the amplitude of the meridional
mid-level jet to the east of the low, and spatial/temporal spread
appears to have increased with evolution of surface cyclogenesis
over the northern High Plains. It is plausible that a meso-alpha
scale corridor of 15 percent severe probabilities may be warranted
in later outlooks, somewhere in the eastern MT/WY to western Dakotas
vicinity.

The large spread in guidance with the development of a near-coastal subtropical/tropical cyclone on D3 renders minimal predictability
for D4 severe potential in NC and the Lower Mid-Atlantic region.

...D6-8...
Latest guidance has trended towards a slower, positive-tilt
large-scale trough evolution over the West, as the next upstream
shortwave impulse digs back into the Southwest. A moderate mid-level southwesterly flow regime and persistent moderate to well-above
normal temperatures may yield daily bouts of low-probability severe
from the south-central High Plains to the Upper Midwest. Despite
typical predictability concerns in this time frame, overall setup
appears unlikely to support a synoptically evident severe episode.

..Grams.. 09/14/2024

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ACUS48 KWNS 150835
SWOD48
SPC AC 150834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0334 AM CDT Sun Sep 15 2024

Valid 181200Z - 231200Z

...DISCUSSION...
A shortwave trough near the northern High Plains at 12Z Wednesday
should slow as it largely progresses across the southern Prairie
Provinces. A belt of enhanced mid-level southwesterlies should
linger over the northern Great Plains through Thursday, and aid in a
recharging and downstream advection of steep mid-level lapse rates
over the Dakotas and NE. The low-level moisture plume near the edge
of the EML should be confined, as dry conditions persist in the
Great Lakes region, on the backside of the low-amplitude mid-level
trough over the East. Low-probability severe may occur along a
portion of a weak cold front on Thursday in the north-central
states.

The next shortwave trough that amplifies into the Southwest should
remain positive tilt and slow moving, until around next weekend when
guidance consensus suggests it accelerates northeastward as another
shortwave trough digs into the Northwest. This pattern should yield
more muted mid-level lapse rates over most of the Great Plains,
especially into next weekend. As such, severe probabilities may
remain low through the period.

..Grams.. 09/15/2024

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ACUS48 KWNS 160854
SWOD48
SPC AC 160853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0353 AM CDT Mon Sep 16 2024

Valid 191200Z - 241200Z

...DISCUSSION...
...D4/Upper Midwest...
Lower-end severe potential remains evident on Thursday afternoon to
evening across a focused portion of the Upper Midwest, centered on
the eastern Dakotas to western MN per latest guidance. A shortwave
trough over the southern Prairie Provinces into the northern Great
Plains should gradually move east. An attendant north/south-oriented
cold front should similarly progress across the Dakotas towards
western MN. In the mid-levels, a plume of steep lapse rates should
be coincident with a belt of enhanced west-southwesterly flow. The
warm-moist sector ahead of the front will likely be confined with
decreasing boundary-layer moisture along/east of the Upper MS
Valley. As such, the overall threat area will probably be fairly
narrow and predictability is too low for a 15 percent highlight.

...D6-7/Southern High Plains to Mid-MO Valley...
The next shortwave trough that amplifies into the Southwest should
remain positive tilt and slow moving, until the weekend when
guidance consensus suggests it accelerates northeastward. The
attendant belt of enhanced mid-level flow around this trough appears
spatially confined, as a ridge dominates from the Lower Rio Grande
Valley to southeast Canada. Coupled with muted mid-level lapse rates
over most of the Great Plains, severe potential appears marginal.

..Grams.. 09/16/2024

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ACUS48 KWNS 170856
SWOD48
SPC AC 170855

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CDT Tue Sep 17 2024

Valid 201200Z - 251200Z

...DISCUSSION...
A shortwave trough that amplifies into the Southwest should remain
positive tilt and slow moving into this weekend. Guidance has
trended towards greater consistency with the evolution of its
attendant belt of enhanced mid-level flow ahead of the trough. Based
on current timing, a focused corridor of severe potential may
develop on D5/Saturday afternoon in the southern High Plains. With a
stout mid-level anticyclone anchored over south TX and 500-mb
temperatures warmer than -2 C across roughly the southeast
two-thirds of TX, a potential corridor of 15 percent probabilities
would likely be confined to the mesoscale. Predictability is too low
to confidently highlight such a corridor at this temporal scale.
After D5, predictability on the synoptic scale wanes considerably.
Guidance spread becomes large with the evolution of northern-stream
shortwave troughs and their influence on this southern-stream wave.

..Grams.. 09/17/2024

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ACUS48 KWNS 180856
SWOD48
SPC AC 180854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Wed Sep 18 2024

Valid 211200Z - 261200Z

...DISCUSSION...
Lower-end severe potential should return on D4/Saturday in advance
of a southern-stream shortwave trough over the Southwest. A
mid-level jetlet, with 500-mb winds from 50-60 kts, is progged to
eject across NM as the shortwave trough reaches the Four Corners
area. A mesoscale corridor of severe storms might develop Saturday
afternoon across a part of eastern NM or Far West TX. The expected
buoyancy plume should be modest in amplitude and rather confined
spatially owing to mid-level temperatures warmer than -3 C at 500 mb
across much of TX.

This shortwave trough may weaken slightly as it progresses towards
the central Great Plains on D5/Sunday. But moderate mid-level
southwesterlies may overspread a plume of rich low-level moisture
arcing to the west-northwest from the Mid/Lower MS Valley. A
mesoscale corridor of focused severe potential could develop in
parts of KS/NE to western MO.

Predictability for each scenario on D4-5 remains too low to
confidently delineate a 15 percent area at these spatiotemporal
scales. Larger-scale pattern predictability becomes too low into
early next week.

..Grams.. 09/18/2024

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ACUS48 KWNS 190857
SWOD48
SPC AC 190856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Thu Sep 19 2024

Valid 221200Z - 271200Z

...DISCUSSION...
Some severe potential is evident on both D4/Sunday and D5/Monday.
But both regimes appear to be focused on the mesoscale, rendering
insufficient predictability at this time frame for a 15 percent
highlight. A combination of both low predictability and potential is
apparent mid-week next week.

A southern-stream shortwave trough is expected to progress from the
Southwest into the central Great Plains on D4. A confined belt of
enhanced mid-level southwesterlies overspreading a corridor of rich boundary-layer moisture just ahead of an attendant weak surface
cyclone may yield a severe-storm threat on Sunday afternoon. Per
consensus of latest guidance, the most favored area could be
centered around the Lower MO Valley. This shortwave trough may
continue northeastward towards the Upper MS Valley into D5. Guidance
spread increases with the degree of forward speed, along with
potential weakening of the flow fields surrounding the trough.
Still, a similar setup may occur on Monday in parts of the Midwest,
centered on the southwest Great Lakes region. Mid-level lapse rates
on both days are uniformly depicted to be weak, suggestive of
lower-end severe potential.

..Grams.. 09/19/2024

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ACUS48 KWNS 200733
SWOD48
SPC AC 200731

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0231 AM CDT Fri Sep 20 2024

Valid 231200Z - 281200Z

...DISCUSSION...
Th latest suite of forecast guidance continues to show large spread
during the Day 4-8/Mon-Fri period. While the evolution of a central
U.S. upper trough is uncertain, it seems likely general troughing
across the eastern half of the U.S. will develop. Some severe
potential could develop around Days 4-5/Mon-Tue from the Midwest to
the Mid-Atlantic as a surface cold front advances east into a
seasonally moist airmass amid moderately enhanced mid/upper flow.
Severe potential should decrease late in the forecast period as the
surface trough moves offshore the Atlantic and Gulf coasts and
surface high pressure builds across the Midwest.

..Leitman.. 09/20/2024

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ACUS48 KWNS 210754
SWOD48
SPC AC 210752

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 AM CDT Sat Sep 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
Forecast confidence is low during the Day 4-8 period as large spread
is evident across medium range forecast guidance. Some low-end
severe potential (sub-15 percent) may continue into Day 4/Tuesday
over parts of the OH/TN Valleys and adjacent Appalachians as a
surface cold front continue to progress east amid modest mid/upper
level southwesterly flow. Thereafter, guidance suggests a cut-off
upper low will develop over some part of the central section of the
CONUS, though confidence is the evolution of this feature is low.
Despite this uncertainty, severe potential appears low beyond Day
4/Tuesday given prior cold frontal passage and limited Gulf return
flow.

..Leitman.. 09/21/2024

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ACUS48 KWNS 220836
SWOD48
SPC AC 220835

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0335 AM CDT Sun Sep 22 2024

Valid 251200Z - 301200Z

...DISCUSSION...
Large spread among guidance is apparent during the Day 4-8 period.
Most guidance develops an upper cyclone over the central or eastern
U.S. for much of the period, while an upper ridge persists over the
western states. However, the GFS suite of guidance is much more
progressive with the central/eastern upper trough/low compared to
the ECMWF, and eventually develops a broad upper ridge over much of
the CONUS late in the period. Given vastly different forecast
solutions, confidence in any severe potential developing during the
forecast period is low.

..Leitman.. 09/22/2024

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ACUS48 KWNS 230843
SWOD48
SPC AC 230842

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0342 AM CDT Mon Sep 23 2024

Valid 261200Z - 011200Z

...DISCUSSION...
Some severe potential may develop over parts of the South/Southeast
on Day 4/Thu in relation to the potential tropical cyclone currently
over the western Caribbean. Uncertainty in the evolution/track of
this system precludes severe probabilities at this time. Beyond Day
4/Thu, increasing spread among forecast guidance and a somewhat
anomalous mid/upper level pattern lends to low predictability.
However, while uncertainty exists regarding the overall evolution of
an eastern upper trough/cut-off cyclone, severe potential in general
appears low given potential for widespread rainfall along with poor
lapse rates/instability.

..Leitman.. 09/23/2024

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