SPC AC 211955

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0255 PM CDT Mon Apr 21 2025

   Valid 212000Z - 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.

   ...20Z Update...
   The Marginal risk in the Lower Great Lakes was trimmed behind the
   eastward-moving frontal band of convection. Elsewhere, the forecast
   remains on track and minimal changes were made with this update. For
   details on the near-term severe risk, reference MCDs #512 and #513.

   ..Weinman.. 04/21/2025

   .PREV DISCUSSION... /ISSUED 1124 AM CDT Mon Apr 21 2025/

   ...Upper OH Valley...
   Morning surface analysis and satellite imagery show a cold front
   sweeping eastward across OH.  Considerable cloud cover is present
   ahead of the front, but a narrow corridor of heating immediately
   ahead of the front will allow a period of heating - promoting
   scattered thunderstorms.  Low-level moisture is limited with
   dewpoints only in the 50s, and forecast soundings show CAPE values
   generally below 1000 J/kg.  Nevertheless, strong low and mid-level
   winds and considerable vertical shear will promote a risk of a few
   organized/severe storms capable of damaging wind gusts and perhaps a
   tornado or two.  Refer to upcoming MCD #511 for further details.

   ...LA/MS/AL/GA/TN...
   The aforementioned surface cold front extends southeastward across
   west TN.  A relatively moist air mass is present ahead of the front
   from southeast LA into parts of MS/AL and middle/east TN, although
   considerable cloud cover will limit heating.  Most 12z models
   suggest scattered thunderstorms will form in this zone during the
   late afternoon and evening, with sufficient CAPE for a few robust
   updrafts.  Low and mid level winds are not particularly strong, and
   large scale forcing is weak.  This should limit the overall
   organization and severity of storms, but a few cells may produce
   gusty winds and hail.

   ...SD...
   Water vapor imagery shows a mid-level shortwave trough over WY
   approaching SD.  Forcing ahead of this feature will likely lead to
   scattered high-based showers and thunderstorms across eastern WY and
   western/central SD this afternoon and evening.  There is some chance
   that a storm or two could produce locally damaging wind gusts.

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