770  
ACUS48 KWNS 190856  
SWOD48  
SPC AC 190854  
 
DAY 4-8 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0354 AM CDT MON APR 19 2021  
 
VALID 221200Z - 271200Z  
   
..DISCUSSION
 
 
A SHORTWAVE TROUGH SHOULD MOVE EASTWARD ACROSS THE SOUTHWEST ON DAY  
4/THURSDAY. LOW-LEVEL MOISTURE RETURN APPEARS LIKELY ACROSS PARTS OF  
THE SOUTHERN PLAINS INTO DAY 5/FRIDAY, AS LEE CYCLOGENESIS OCCURS  
ACROSS THE SOUTHERN HIGH PLAINS AHEAD OF THE APPROACHING UPPER  
TROUGH. RUN-TO-RUN CONSISTENCY OVER THE PAST SEVERAL RUNS OF THE  
DETERMINISTIC ECMWF LENDS CONFIDENCE THAT THE SHORTWAVE TROUGH  
SHOULD EJECT EASTWARD OVER THE SOUTHERN PLAINS ON FRIDAY. INCREASING  
LOW-LEVEL MOISTURE TO THE EAST OF A DRYLINE/COLD FRONT AND STEEP  
MID-LEVEL LAPSE RATES SHOULD SUPPORT AT LEAST MODERATE INSTABILITY  
IN A CORRIDOR ACROSS PARTS OF OK AND TX BY FRIDAY AFTERNOON. STRONG  
MID-LEVEL FLOW AND RELATED DEEP-LAYER SHEAR APPEAR MORE THAN  
SUFFICIENT FOR ORGANIZED SEVERE STORMS, INCLUDING SUPERCELLS. AS  
MID-LEVEL HEIGHT FALLS/ASCENT OVERSPREAD THE WARM SECTOR, ROBUST  
CONVECTIVE DEVELOPMENT SHOULD OCCUR, WITH AT LEAST ISOLATED SEVERE  
STORMS POTENTIALLY SPREADING EASTWARD TOWARDS SOUTHEAST TX FRIDAY  
EVENING/NIGHT. CONFIDENCE IN THIS SCENARIO OCCURRING HAS INCREASED  
ENOUGH TO INCLUDE A 15% SEVERE AREA FOR FRIDAY.  
 
SOME SEVERE RISK MAY CONTINUE ACROSS PARTS OF THE LOWER MS VALLEY  
AND SOUTHEAST LATE FRIDAY NIGHT INTO THIS UPCOMING WEEKEND, BUT  
DETAILS REGARDING THE EASTWARD PROGRESSION OF THE UPPER TROUGH AND  
SUBSEQUENT CONVECTIVE EVOLUTION REMAIN UNCLEAR. IF A SEVERE THREAT  
DOES DEVELOP, THEN IT MAY FOCUS ALONG/NEAR PARTS OF THE CENTRAL GULF  
COAST ON DAY 6/SATURDAY WHERE LOW-LEVEL MOISTURE RETURN IS FORECAST  
TO BE GREATEST. REGARDLESS, CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE  
A 15% SEVERE AREA AT THIS TIME. DEPENDING ON HOW QUICKLY A SURFACE  
COLD FRONT MOVES EASTWARD, A LINGERING SEVERE RISK MAY PERSIST  
ACROSS SOME PORTION OF THE SOUTHEAST INTO DAY 7/SUNDAY. FINALLY,  
MEDIUM-RANGE GUIDANCE SUGGESTS THAT A LARGE-SCALE UPPER TROUGH MAY  
DEVELOP EASTWARD ACROSS THE WESTERN STATES AND TOWARDS THE HIGH  
PLAINS EARLY NEXT WEEK. GRADUALLY INCREASING LOW-LEVEL MOISTURE  
RETURN ACROSS THE PLAINS MAY EVENTUALLY LEAD TO SOME SEVERE RISK,  
BUT PREDICTABILITY IS QUITE LOW AT THIS EXTENDED TIME FRAME.  
 
..GLEASON.. 04/19/2021  
 
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