587
ACUS02 KWNS 141737
SWODY2
SPC AC 141736

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1236 PM CDT Wed May 14 2025

Valid 151200Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
EAST-CENTRAL MINNESOTA INTO MUCH OF WISCONSIN...NORTHEAST
ILLINOIS...SOUTHWEST LOWER MICHIGAN...AND NORTHERN INDIANA...

...SUMMARY...
Severe thunderstorms are expected across parts of the upper
Mississippi River Valley and Great Lakes region Thursday afternoon
and evening. The primary risk with this activity is large to very
large hail, tornadoes (a couple may be strong), and scattered wind
damage.

More isolated severe thunderstorms are expected through the lower
Ohio River Valley, Ozarks Plateau, and parts of the Mid-Atlantic.

...Synopsis...

An upper cyclone centered over the Dakotas, and attendant
negative-tilt shortwave trough will deepen and spread northeast
across the Upper Midwest on Thursday. A belt of enhanced mid/upper
southwesterly flow will overspread the region, with a secondary jet
streak oriented from the southern Plains to the Ohio Valley.

At the surface, low pressure is forecast over eastern SD during the
morning. The deepening surface low will lift north/northeast into
northern MN through much of the forecast period. As this occurs, a
warm front arcing southeast from the low to the Ohio Valley will
lift northward during the afternoon and into the evening. This will
allow a moist warm sector to lift northward across the Upper MS
Valley and Great Lakes vicinity. Extending south from the surface
low, a dryline will be in place from the Mid-MO valley into eastern
OK and central TX. This feature will develop east/northeast across
MN/WI/IA/MO/IL through the evening.

Severe thunderstorm activity is expected near the triple point, and
along the warm front and dryline (where a capping inversion is able
to be overcome).

...Upper Midwest/Great Lakes vicinity...

Convection will likely be ongoing Thursday morning near the surface
low and beneath the upper low. Cold temperatures aloft will support
steepened midlevel lapse rates within modest boundary layer moisture
across the eastern Dakotas. Hail will be possible with this
activity. Supercell wind profiles are also expected into late
morning, and additional low-topped convection may develop from late
morning into early afternoon, posing a risk of hail, gusty winds and
a tornado or two across the eastern Dakotas.

By afternoon, mid-60s F dewpoints are expected within a somewhat
narrow warm sector from central MN southeast into WI and northern
IL. As large-scale ascent increases, thunderstorms are expected to
develop in an arc from east-central MN into southeast WI on the nose
of a 40-50 kt low-level jet and midlevel dry slot. Vertically
veering winds will produce supercell wind profiles. Low-level
hodographs will become enlarged, in part due to the increasing
low-level jet, but also within the warm front zone. Additionally,
steep midlevel lapse rates and MLCAPE greater than 2500 J/kg are
possible. This should support robust updrafts and rapidly increasing
storm intensity once initiation occurs. Large to very large hail (up
to 3 inch diameter) and tornadoes (a couple may be strong) appear
possible within the moisture-rich, favorably sheared warm sector.
Given strong 850-700 mb flow and steepening low-level lapse rates
where strong heating occurs, severe gust potential is also expected.
Current thinking is that given the orthogonal nature of low-level
flow to the surface boundaries, supercell storm mode may be favored,
with perhaps a trend toward bowing segment during the evening. A
gust to 80 mph cannot be ruled out, but given uncertainty in storm
mode transitioning to or favoring linear segments have held off on
adding a sig-wind delineation.

The bands of severe storms should develop northeast with time into
the evening, with a gradual weakening trend expected across Upper
and Lower MI.

...Northern IL/IN into OH/PA vicinity...

Storm coverage is more uncertain with southward extent due to
increasing capping in the 850-700 mb layer, and weaker large-scale
ascent. Nevertheless, isolated to widely scattered storms are
expected to develop during the afternoon in a strongly unstable and
moderately sheared environment. Supercells producing large hail, a
couple of tornadoes and damaging gusts will be possible into the
evening hours across IL/IN. Additional activity is expected to
develop in the low-level warm advection regime during the
evening/overnight hours across portions of OH/western PA. This
activity may remain elevated, but would still pose a risk for hail,
or perhaps isolated gusty winds if clustering occurs.

...Ozarks to Mid-South/Ohio Valley...
Further south from southeast MO/southern IL into KY, modest height
falls are forecast during the evening/overnight hours. This may be
sufficient to either overcome capping, or to allow elevated
convection to develop. Severe storms capable of damaging gusts,large
hail and a tornado or two appear possible, though this risk is a bit
more uncertain/conditional and coverage may be low.

...Mid-Atlantic...

A moist, weakly capped air mass is expected to remain in place
across the Mid-Atlantic through Thursday afternoon. While lapse
rates will be modest after several days of convective overturning,
temperatures warming into the upper 70s/low 80s will promote
sufficient buoyancy for thunderstorm development. Upper ridging
moving into the region will likely limit thunderstorm coverage, but
convection developing along the Blue Ridge Mountains will mature in
an environment with increasing deep-layer shear. A few organized
cells appear possible with an attendant severe hail/wind threat.

..Leitman.. 05/14/2025

$$