591  
ACUS01 KWNS 200533  
SWODY1  
SPC AC 200532  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1232 AM CDT WED MAR 20 2019  
 
VALID 201200Z - 211200Z  
   
..NO SEVERE THUNDERSTORM AREAS FORECAST
 
 
   
..SUMMARY
 
 
ISOLATED THUNDERSTORMS ARE EXPECTED OVER PORTIONS OF CALIFORNIA INTO  
THE SOUTHWESTERN U.S. TODAY AND TONIGHT, AND NEAR THE NORTH  
CAROLINA COAST OVERNIGHT.  
   
..SYNOPSIS
 
 
IN MID/UPPER LEVELS, AN OMEGA PATTERN NOW OVER WESTERN NORTH  
AMERICA, WITH AN INITIALLY CLOSED ANTICYCLONE CENTERED OVER THE  
CANADIAN ROCKIES, WILL BREAK DOWN INTO A HIGH-AMPLITUDE SYNOPTIC  
RIDGE THROUGH THE PERIOD. BY 21/12Z, THE RIDGE SHOULD BE LOCATED  
OVER THE HIGH PLAINS FROM TX TO AB. TO ITS EAST, A STRONG SHORTWAVE  
TROUGH INITIALLY WAS ANALYZED OVER THE CENTRAL PLAINS AND CO WITH A  
WEAK/CLOSED 500-MB LOW OVER NE. AS A NORTHERN-STREAM PERTURBATION  
DIGS SOUTHEASTWARD FROM THE ON/MB BORDER REGION ACROSS THE UPPER  
GREAT LAKES AND AMPLIFIES GREATLY, THE CENTRAL PLAINS TROUGH WILL  
PIVOT SOUTHEASTWARD THEN EASTWARD TO THE SOUTHERN APPALACHIANS,  
WHILE WEAKENING.  
 
MEANWHILE, WEST OF THE SYNOPTIC RIDGE, A SERIES OF SHORTWAVES WILL  
PIVOT THROUGH A NEGATIVELY TILTED SYNOPTIC TROUGH CURRENTLY OFFSHORE  
FROM CA, SHIFTING THE SYNOPTIC TROUGH INLAND THIS AFTERNOON. BY  
21/12Z, THE TROUGH SHOULD BE LOCATED FROM NORTHWESTERN CA  
SOUTHEASTWARD, OBLIQUELY CROSSING THE SIERRA NEVADA TO CENTRAL/  
EASTERN AZ. A BASAL SHORTWAVE TROUGH SHOULD PIVOT OVER NORTHERN  
BAJA AND SOUTHERN CA, ACROSS THE LOWER COLORADO RIVER VALLEY TO  
CENTRAL AZ OVERNIGHT.  
 
AT THE SURFACE, A COLD FRONT WAS ANALYZED FROM A WEAK LOW OVER  
WEST-CENTRAL MO SOUTHWESTWARD ACROSS NORTHEASTERN THROUGH  
SOUTHWESTERN OK, TO SOUTH-CENTRAL NM. BY 00Z THE FRONT SHOULD REACH  
CENTRAL KY, WESTERN/MIDDLE TN, NORTHWESTERN LA, AND SOUTH-CENTRAL  
TX. AS THE RELATED MID/UPPER WAVE WEAKENS OVERNIGHT, SO WILL THE  
FRONT, WHICH SHOULD EXTEND FROM THE SOUTHERN APPALACHIANS TO THE  
NORTHWESTERN GULF BY 21/12Z. WITH BOTH MID/UPPER TROUGHS  
APPROACHING THE REGION, SURFACE CYCLOGENESIS SHOULD OCCUR BY 00Z  
OFFSHORE FROM SC. THAT LOW SHOULD MOVE GENERALLY NORTHWARD OVER THE  
TIDEWATER REGION OF EASTERN NC OVERNIGHT.  
   
..SOUTHWESTERN CONUS
 
 
A BROAD AREA OF ISOLATED THUNDER POTENTIAL IS EVIDENT THROUGH MUCH  
OF THE PERIOD, AS COLD AIR ALOFT AND STEEPENING MIDLEVEL LAPSE RATES  
SPREAD INLAND AHEAD OF THE SYNOPTIC TROUGH, AND SHOTS OF MORE  
FOCUSED MID/UPPER FORCING PRECEDE THE EMBEDDED SHORTWAVE  
PERTURBATIONS. LIGHTNING PRODUCTION THEREFORE SHOULD BE EPISODIC  
AND SOMEWHAT STREAKY, AND LIKELY RATHER DISCONTINUOUS IN SPACE AND  
TIME ACROSS THE OUTLOOK AREA. THE AZ/NM THUNDER POTENTIAL WILL BE  
WEIGHTED MORE TOWARD THE LATTER HALF OF THE PERIOD. BUOYANCY IS  
FORECAST TO BE MARGINAL REGION-WIDE, WITH MUCAPE LESS THAN 300 J/KG  
OVER MOST OF THE AREA. HOWEVER, FORECAST SOUNDINGS SUGGEST  
OCCASIONAL EXTENSION OF THAT WEAK CAPE INTO PROSPECTIVE LIGHTNING-  
PRODUCTION LAYERS.  
   
..COASTAL NC
 
 
ISOLATED THUNDERSTORMS ARE POSSIBLE OVERNIGHT ACROSS THIS AREA. THE  
GREATEST COVERAGE MAY BE OFFSHORE WHERE LOW-LEVEL THETA-E IS RICHER;  
HOWEVER, ELEVATED BUOYANCY MAY BECOME DEEP AND STRONG ENOUGH TO  
SUPPORT THUNDER INLAND. THE SURFACE LOW IS PROGGED TO MOVE THROUGH  
A STABLE BOUNDARY LAYER, BENEATH A ZONE OF LOW-LEVEL WARM ADVECTION  
AND MOISTURE TRANSPORT DEVELOPING IN THE MASS RESPONSE TO THE  
APPROACHING SHORTWAVE TROUGH(S). BENEATH THE LEFT-EXIT REGION OF  
THE UPPER-LEVEL JET STREAK, A 50-60-KT LLJ IS FORECAST TO DEVELOP  
OVERNIGHT AROUND THE EASTERN SECTOR OF THE 850-MB CYCLONE, WHICH  
WILL BE SOMEWHAT FARTHER INLAND THAN ITS SURFACE MANIFESTATION.  
TIME SERIES OF FORECAST SOUNDINGS INDICATE THE RESULTANT INCREASE IN  
THETA-E ABOVE THE BOUNDARY LAYER WILL SUPPORT UP TO ABOUT 700 J/KG  
MUCAPE OVER LAND, SOMETIMES EXTENDING INTO ICING LAYERS SUITABLE FOR  
LIGHTNING PRODUCTION.  
   
..AR AND MID-SOUTH
 
 
A NARROW SPATIAL/TEMPORAL WINDOW FOR THUNDER MAY FORM OVER THE  
REGION DURING LATE AFTERNOON INTO EARLY EVENING, AND ISOLATED  
LIGHTNING CANNOT BE RULED OUT. HOWEVER, THE POTENTIAL CURRENTLY  
APPEARS TOO MARGINAL AND CONDITIONAL FOR A 10%/CATEGORICAL AREAL  
LINE. OFFSETTING FACTORS REGARDING THUNDER POTENTIAL INCLUDE:  
* FAVORABLE -- WEAK MOISTENING OF LOW LEVELS, AND STEEPENING OF  
LAPSE RATES FROM BOTH LOW-LEVEL WARM ADVECTION AND A WELL-DEFINED  
SWATH OF DCVA/COOLING ALOFT AHEAD OF THE MID/UPPER PERTURBATION;  
* UNFAVORABLE -- WEAKENING OF THE TROUGH ALOFT AND ASSOCIATED  
LOW-LEVEL MASS RESPONSE/LIFT WITH TIME, LOW-LEVEL FRONTOLYSIS IN THE  
LATTER HALF OF THE PERIOD, AND LACK OF BOTH MORE ROBUST MOISTURE AND  
DEEPER BUOYANCY.  
 
A THUNDER AREA MAY NEED TO BE INTRODUCED IN A FUTURE UPDATE IF THE  
POTENTIAL GETS BETTER-FOCUSED AND MORE CONSISTENT IN PROGS.  
 
..EDWARDS/GLEASON.. 03/20/2019  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SPC Page Main Text Page