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
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