SWODY2
SPC AC 281728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT FRI MAY 28 2010
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NRN AND
CENTRAL PLAINS...
...NRN AND CENTRAL PLAINS...
MODELS ARE IN AGREEMENT SHOWING THE NRN EXTENT OF THE WRN U.S.
TROUGH EVOLVING INTO A CLOSED LOW ON SATURDAY...MOVING NWD FROM MT
INTO ALBERTA/SASKATCHEWAN. A SHORTWAVE TROUGH WITHIN THE BASE OF
THE PARENT MID/UPPER LEVEL TROUGH WILL TRACK NEWD FROM THE SRN GREAT
BASIN TO THE NRN PLAINS BY 12Z SUNDAY. A COLD FRONT EXTENDING SSWWD
FROM CENTRAL ND TO NERN CO AT 12Z SATURDAY WILL ADVANCE EWD ACROSS
THE DAKOTAS AND NEB TO WRN KS THIS FORECAST PERIOD.
NO CHANGES ARE NEEDED ACROSS SLIGHT RISK AREA ISSUED IN THE INITIAL
DAY 2 OUTLOOK. MOIST AXIS CURRENTLY EXTENDING NWD THROUGH THE CNTRL
AND NRN PLAINS WILL PERSIST IN PRE-FRONTAL WARM SECTOR WITH
DEWPOINTS GENERALLY IN THE LOWER 60S. STEEP LAPSE RATES EXTENDING
NEWD INTO THIS REGION AND DIABATIC WARMING OF BOUNDARY LAYER WILL
CONTRIBUTE TO MODERATE INSTABILITY WITH 2000-2500 J/KG MLCAPE
LIKELY. THE CAP WILL ACT TO SUPPRESS DEEP CONVECTION UNTIL MID-LATE
AFTERNOON WHEN THE DESTABILIZING BOUNDARY LAYER AND FRONTAL
CONVERGENCE SHOULD PROMOTE TSTM INITIATION. MODELS CONTINUE TO
INDICATE STRONGER MID-UPPER LEVEL FLOW ASSOCIATED WITH THE NWD
EJECTING UPPER JET WILL REMAIN WITHIN AND BEHIND FRONTAL ZONE WITH
GENERALLY MODEST DEEP LAYER FLOW AND 25-35 KT 0-6 KM SHEAR IN MOST
OF WARM SECTOR. WIND PROFILES WILL BE SUFFICIENT FOR ORGANIZED
STORM STRUCTURES WITHIN THE FRONTAL ZONE. STORMS SHOULD EVENTUALLY
GROW UPSCALE INTO LINES AND CLUSTERS DURING THE EVENING. LARGE HAIL
AND DAMAGING WIND ARE EXPECTED TO BE THE MAIN THREATS. THOUGH...A
TORNADO THREAT MAY EXIST OVER PARTS OF ERN ND IN THE VICINITY OF A
SURFACE LOW WHERE LOW LEVEL SHEAR SHOULD BE ENHANCED.
...TN/LOWER MS VALLEYS TO SERN STATES...
MODELS SUGGEST A BROAD...WEAK CLOSED LOW WILL EXTEND FROM THE LOWER
MS VALLEY TO THE SERN STATES ON SATURDAY. TSTM COVERAGE ON DAY 2
SHOULD BE GREATEST IN ASSOCIATION TO A WEAK UPPER LOW/ VORTICITY
CENTER DRIFTING SLOWLY SSEWD FROM THE LOWER MS VALLEY TO THE CENTRAL
GULF COAST...WITH ACTIVITY EXTENDING SWD FROM THE TN VALLEY TO THE
GULF COAST AND FL. ALTHOUGH MODERATE INSTABILITY IS EXPECTED ACROSS
MUCH OF THIS REGION...WEAK DEEP LAYER SHEAR WILL TEND TO LIMIT STORM
ORGANIZATION WITH MORE PULSE-TYPE STORMS POSSIBLE. GREATER DEEP
LAYER SHEAR MAY OCCUR ACROSS SRN LA ALONG SRN EXTENT OF CLOSED LOW
WHERE MID AND UPPER LEVEL FLOW WILL BE STRONGER. HOWEVER...
UNCERTAINTY IN OVERALL STORM COVERAGE PRECLUDES THE INTRODUCTION OF
HIGHER SEVERE PROBABILITIES AND CATEGORICAL OUTLOOK.
...MD/ERN VA/ERN NC...
BACKDOOR COLD FRONT EXTENDING FROM ERN NC NNWWD TO NRN VA ON DAY 1
IS EXPECTED TO RETREAT EWD ON SATURDAY TOWARD THE MID-ATLANTIC COAST
AS THE SURFACE HIGH CENTERED OFF THE SRN NEW ENGLAND COAST MOVES
FARTHER EWD DURING DAY 2. SURFACE WINDS BECOMING SLY WITH THE
PASSAGE OF THIS FRONT AND AHEAD OF A WEAK SURFACE FRONT ADVANCING
EWD WILL SUPPORT AN INFLUX OF MID 60S DEWPOINTS INTO CENTRAL-ERN
MD...ERN VA AND NERN NC BY SATURDAY AFTERNOON. ALTHOUGH MIDLEVEL
LAPSE RATES WILL BE MODEST /LESS THAN 6.5 C PER KM/...THE INCREASING
BOUNDARY LAYER MOISTURE AND SURFACE HEATING SHOULD SUPPORT MLCAPE
VALUES UP TO 1000 J/KG. FORCING FOR ASCENT ALOFT SHOULD BE WEAK.
HOWEVER...DESTABILIZATION WITHIN A WEAKLY CAPPED AIR MASS IS
EXPECTED TO SUPPORT CONVECTIVE DEVELOPMENT WITHIN THE WARM SECTOR
ALONG AND WEST OF THE RETREATING BOUNDARY. NNWLY MID LEVEL WINDS
/25-40 KT/ ATOP SLY SURFACE WINDS WILL FAVOR EFFECTIVE BULK SHEAR
/25-35 KT/ SUPPORTIVE OF MULTICELLS AND POTENTIALLY A FEW
SUPERCELLS. THE SOMEWHAT MODEST INSTABILITY MAY LIMIT THE OVERALL
SEVERE COVERAGE...AND THUS WILL ONLY INTRODUCE LOW SEVERE
PROBABILITIES AT THIS TIME FOR THE ERN EXTENT OF THE MID-ATLANTIC
STATES.
..PETERS.. 05/28/2010
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