ACUS01 KWNS 141959
SWODY1
SPC AC 141958
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Fri Mar 14 2025
Valid 142000Z - 151200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THE LOWER/MID
MISSISSIPPI VALLEY INTO THE LOWER OHIO VALLEY...
...SUMMARY...
A regional outbreak of severe thunderstorms is likely this afternoon
through tonight across parts of the Lower/Mid Mississippi Valley and
portions of the Lower Ohio Valley and Mid-South. Numerous tornadoes,
several of which could be strong to intense, widespread severe gusts
ranging from 60 to 100 mph, and scattered large hail up to baseball
size all appear likely.
...20z Update...
Widespread significant severe weather remains likely this afternoon
through tonight over much of the MS Valley and parts of the
Southeast.
An intense, negative-tilt upper trough and 120 kt mid-level jet will
rapidly eject northeastward over the central Plains through the day.
An associated deep surface low over western KS will continue to
intensify as it lifts east/northeast tonight. Initial updrafts along
a bent back dryline from northeastern KS, far eastern OK, and
western MO will spread northeastward into a warm and rapidly
moistening air mass over the MO Valley. While initial dewpoints are
quite limited, (40s F) very steep low and mid-level lapse rates and
a rapid surge of low-level moisture is likely later this
afternoon/evening. A broken line of initially high-based storms will
quickly spread eastward within very strong tropospheric flow.
Efficient downward momentum transport will support widespread
damaging gusts, potentially as high as 80-100 mph.
Ahead of these storms, low-level dewpoints should rapidly surge into
the 50s and low 60s F. Lowering cloud bases, and very strong mid and
low-level shear will allow for a few semi-discrete/embedded
supercells to form/mature over eastern MO, southern IA, western IL
and northern AR. A tornado threat (some strong to intense), is
likely to develop with these storms through the late afternoon and
evening hours, along with a continued risk for damaging winds and
large hail.
Farther south over parts of the ArkLaMiss and southwest TN,
scattered storms are expected to evolve within a strong low-level
warm air advection regime and ahead of the Pacific front. Dewpoints
in the mid 60s F will quickly lift northward over northern LA,
southern AR, into central MS. While forcing for ascent is likely to
be more nebulous, strong low-level flow within a 45-60 kt low-level
jet will support significant hodograph enlargement and sufficient moisture/buoyancy for strong supercells. Recent CAM guidance has
come into better agreement on the positioning/timing of a cluster of
likely supercells evolving across northern LA and west-central MS
later this evening. Given the intensifying wind fields, and STP
environment of 3-4, strong tornadoes appear more likely through the
evening and into the overnight hours. Given increased confidence in
the development of intense supercells, have adjusted the Moderate
area farther south and west over MS/LA/AR.
..Lyons.. 03/14/2025
.PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Mar 14 2025/
...Synopsis...
Water-vapor imagery late this morning indicates a powerful and
negatively tilted mid/upper-level shortwave trough over the southern
High Plains. An intense mid-level jet (with winds of 100-115+ kt at
500 mb) will continue to round the base of the trough, and quickly
eject northeastward across OK and eastern KS this afternoon. This
mid-level jet will move over parts of the mid MS Valley and Midwest
this evening and tonight in tandem with the northeastward-advancing
shortwave trough. Strong ascent aloft associated with both of these
features will overspread portions of the central CONUS as a deep
surface cyclone develops northeastward from the central High Plains
into the Upper Midwest this afternoon through tonight. In the low
levels, a dryline will surge eastward across the southern/central
Plains through the day, eventually arcing from the low southeastward
into the Ozarks. A large area of significant severe potential
remains evident across parts of the lower/mid MS Valley into the
Midwest and Mid-South.
...Mid Mississippi Valley into the Midwest and Mid-South...
Ample diurnal heating is expected through this afternoon ahead of
the cyclone, with elevated convection already occurring across parts
of eastern OK into southeast KS and southwest MO. More robust,
surface-based thunderstorms will likely develop by early/mid
afternoon (18-21z) along/east of the dryline from parts of eastern
NE southward into eastern KS/western MO, as a southerly low-level
jet attempts to bring shallow boundary-layer moisture northward into
the mid MS Valley and vicinity. The northern portion of this
convection will be oriented more orthogonal to the ejecting
mid-level jet, and current expectations are for quick upscale growth
into a fast northeastward-moving band, posing a risk for widespread severe/damaging winds as this activity moves into IA and towards the
MO/IA/IL border region. Given the strength of the low/mid-level flow
and presence of steep lapse rates aloft, along with a well-mixed
boundary layer, intense thunderstorm straight-line gusts peaking
locally in the 80-100 mph range are possible with the stronger cores/inflections in the band as it matures and moves across parts
of the mid MS Valley, and eventually into the southwestern Great
Lakes this evening through tonight.
Additional, potentially more discrete, severe thunderstorms will
develop this afternoon farther southeast along the wind shift into central/eastern MO, generally on the northern periphery of somewhat
better low-level moisture from southeast MO southward into the
Mid-South. Stronger high-level flow and ample deep-layer shear over
these will likely promote at least semi-discrete supercells. Latest
model guidance, including various convection-allowing HREF members,
suggest scattered supercells developing late this afternoon and
evening as far south as the MS/AR/TN border region. Have nudged
severe probabilities and the corresponding SLGT/ENH/MDT westward a
little in western/central MO to account for a slightly earlier
initiation. Various NAM/RAP forecast soundings strongly favor
intense supercells capable of large to very large hail (up to 2-3
inches in diameter), and potentially multiple strong to intense
tornadoes this evening as effective SRH rapidly increases in tandem
with a southerly low-level jet strengthening to 50-65+ kt. This
substantial severe threat is expected to continue eastward overnight
into parts of the lower OH Valley/Midwest, before convection
eventually outpaces the low-level moisture return and weakens.
...Lower Mississippi Valley...
Large-scale forcing for ascent appears a bit more nebulous/weak
farther south into the lower MS Valley. Still, the 12Z suite of
guidance shows some potential for surface-based thunderstorms
developing by late this afternoon across the ArkLaMiss region. While
the stronger low/mid-level flow and forcing are expected to remain
to the north of this region, greater low-level moisture and related
instability will be present. This favorable thermodynamic and
kinematic environment will support supercells, with associated
threat for large to very large hail, damaging winds, and tornadoes.
Some of tornadoes could be strong this evening with any sustained
supercells, especially across central MS and vicinity. Have expanded
the ENH to account for this potential, and consideration was given
to expanding the MDT southward into central MS as well. But, there
is still some uncertainty with overall thunderstorm coverage.
$$
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