SPC AC 211230

   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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