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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