425  
ACUS01 KWNS 240052  
SWODY1  
SPC AC 240051  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0751 PM CDT WED SEP 23 2020  
 
VALID 240100Z - 241200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ISOLATED STRONG  
STORMS MAY POSE SOME RISK FOR SEVERE WEATHER TONIGHT ACROSS PARTS OF  
CENTRAL AND SOUTHERN MISSISSIPPI...PORTIONS OF THE UPPER  
MIDWEST...AND WEST OF THE WASHINGTON CASCADES...  
   
..SUMMARY
 
 
THUNDERSTORM ACTIVITY WHICH COULD POSE AT LEAST SOME RISK FOR A  
TORNADO MAY PERSIST TONIGHT ACROSS PARTS OF CENTRAL AND SOUTHERN  
MISSISSIPPI.  
   
..01Z OUTLOOK UPDATE
 
 
   
..LOWER MISSISSIPPI VALLEY
 
 
THUNDERSTORM ACTIVITY HAS GENERALLY BEEN CONFINED TO A SHORT NARROW  
BAND, JUST IN ADVANCE OF THE CENTER OF BETA, APPARENTLY AIDED BY A  
WEAK MID-LEVEL THERMAL TROUGH (AS SUGGESTED BY THE RAPID REFRESH  
NEAR/JUST ABOVE 700 MB). AS THE SURFACE LOW CENTER OF BETA MIGRATES  
ACROSS THE MISSISSIPPI RIVER INTO SOUTHWEST/WEST CENTRAL MISSISSIPPI  
OVERNIGHT, IT IS POSSIBLE THAT THIS MAY CONTINUE. SUPPORTED BY  
INFLOW OF BOUNDARY-LAYER MOISTURE CHARACTERIZED BY LOWER/MID 70S F  
DEW POINTS, IN THE PRESENCE OF MODEST CLOCKWISE CURVED LOW-LEVEL  
HODOGRAPHS, IT IS POSSIBLE THAT THERE COULD BE OCCASIONAL LOW-LEVEL  
MESOCYCLONE STRENGTHENING WHICH COULD POSE AT LEAST SOME RISK FOR A  
TORNADO.  
 
   
..ELSEWHERE
 
 
...THUNDERSTORM ACTIVITY MAY CONTINUE TO INCREASE THIS EVENING, INTO  
THE OVERNIGHT HOURS, WITHIN A NARROW CORRIDOR ALONG A FRONTAL ZONE  
ACROSS PARTS OF NORTH CENTRAL MINNESOTA INTO NORTHERN WISCONSIN AND  
ADJACENT UPPER MICHIGAN. THIS MAY BE AIDED BY FORCING ASSOCIATED  
WITH A SHORT WAVE TROUGH DIGGING INTO THE REGION, AND ITS POSSIBLE  
THAT THERMODYNAMIC PROFILES AND CLOUD-BEARING LAYER SHEAR MAY BE  
MARGINALLY CONDUCIVE FROM SOME HAIL AND GUSTY WINDS IN STRONGER  
STORMS.  
 
...ISOLATED THUNDERSTORM DEVELOPMENT HAS ALSO OCCUR AHEAD OF THE  
DIGGING MID-LEVEL TROUGH ACROSS PARTS OF THE WESTERN DAKOTAS, WHERE  
BOUNDARY-LAYER INSTABILITY LARGELY DRIVEN BY DAYTIME HEATING BECAME  
LOCALLY MAXIMIZED. THIS ACTIVITY IS NOW WANING NORTH/NORTHEAST OF  
THE BLACK HILLS VICINITY, BUT COULD PERHAPS CONTINUE INTO THE 02-04Z  
TIME FRAME.  
 
...AS THE BASE OF A 500 MB THERMAL TROUGH WITH TEMPERATURES NEAR OR  
BELOW -20C MIGRATES INLAND, SCATTERED THUNDERSTORM DEVELOPMENT  
APPEARS INCREASINGLY POSSIBLE WEST OF THE WASHINGTON CASCADES BY  
04-06Z. IT IS POSSIBLE THAT BOUNDARY-LAYER INSTABILITY MAY BECOME  
MARGINALLY SUFFICIENT, IN THE PRESENCE OF MODERATE TO STRONG  
DEEP-LAYER MEAN FLOW AND SHEAR, TO SUPPORT SOME RISK FOR HAIL AND  
GUSTY WINDS IN STRONGER ACTIVITY.  
 
..KERR.. 09/24/2020  
 

 
 
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