SPC Apr 21, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0730 AM CDT Mon Apr 21 2025

Valid 211300Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER OHIO VALLEY AND LOWER GREAT LAKES...AND PORTIONS OF THE
SOUTHEAST...

...SUMMARY...
Isolated strong to severe thunderstorms are possible today across
the upper Ohio Valley/lower Great Lakes and parts of the Southeast.
Damaging winds and marginally severe hail are the primary risks.

...Upper Ohio Valley to the Lower Great Lakes...
An upper trough with an attendant 55-70 kt mid-level jet will
advance east-northeastward from the Upper Midwest across the Great
Lakes and Northeast today. A related surface low will develop
northeastward into Ontario/Quebec, while a cold front sweeps
eastward over the OH Valley and parts of the Mid-Atlantic and
Northeast through this evening. Modest low-level moisture will
advect northward ahead of this front in tandem with a strong
southwesterly low-level jet. Even though this moisture will remain
somewhat limited, filtered daytime heating and cool mid-level
temperatures should aid weak destabilization in a narrow corridor
along/ahead of the front by early afternoon. Thunderstorms that
develop along the front may pose an isolated severe/damaging wind
threat this afternoon and early evening given the expected strength
of the low/mid-level flow. Occasional hail may also be noted with
the strongest cores, and sufficient low-level shear should exist to
support a tornado or two. The Marginal Risk has been expanded
northward/eastward some based on latest guidance trends regarding
sufficient destabilization to support surface-based convection.

...Southeast...
The trailing portion of the surface cold front should make only slow
east-southeastward progress today across the Southeast. This region
will have weaker low/mid-level winds compared to locations farther
north. Still, around 500-1500 J/kg of MLCAPE should develop by this
afternoon along/ahead of the front, while 25-35 kt of deep-layer
shear aids in modest updraft organization. Any thunderstorms which
develop in this regime could pose an isolated threat for marginally
severe hail and damaging winds. This threat should peak by mid
afternoon, before gradually diminishing through the evening with the
loss of daytime heating.

...Northern Plains...
Gusty winds may occur with high-based convection this afternoon as a
shortwave trough moves eastward over the northern Plains. However,
low-level moisture and instability are both expected to remain very
meager, which should preclude an organized severe wind threat.

...Upper Midwest...
Elevated thunderstorms may develop late tonight across parts of IA
in a low-level warm advection regime. With MUCAPE forecast to remain
less than 1000 J/kg, the potential for severe hail appears too
limited to include low severe probabilities at this time.

..Gleason/Broyles.. 04/21/2025

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