SWODY1
SPC AC 201626
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1126 AM CDT TUE MAY 20 2008
VALID 201630Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN VA/CAROLINAS SWWD
ACROSS THE SRN APPALACHIANS TOWARD THE LOWER MS VALLEY......
...MID ATLANTIC AND SERN STATES...
DEEP POLAR UPPER LOW REMAINS OVER SERN CANADA WITH A STRONG CYCLONIC
JET FROM OH VALLEY TO OFFSHORE MID ATLANTIC STATES. EMBEDDED S/W
TROUGH RACES EWD ACROSS VA/NC THIS AFTERNOON. DEEPENING SURFACE LOW
DELMARVA AREA THIS MORNING MOVES OFFSHORE WITH TRAILING COLD FRONT
WSWWD INTO TN VALLEY MOVING SEWD THRU THE CAROLINAS TONIGHT AND THEN
EXTENDING WWD THRU GULF STATES.
A PLUME OF STEEP MID LEVEL LAPSE RATES HAVE SPREAD EWD AHEAD OF
FRONT IN THE WESTERLY FLOW AND COUPLED WITH A MOISTURE PLUME WITH
PW/S IN EXCESS OF AN INCH PROVIDES AN ENVIRONMENT FOR SEVERE
THUNDERSTORMS ONCE THE HEATING DISSIPATES THE CURRENT CONVECTIVE
INHIBITION IN THE WARM SECTOR.
WITH THE STRONG SHEAR IN PLACE ACROSS MID ATLANTIC STATES E OF
APPALACHIANS...THUNDERSTORMS EXPECTED TO RAPIDLY BECOME SEVERE THIS
AFTERNOON. INITIAL THUNDERSTORMS EXPECTED SRN/SERN VA/NRN NC EARLY
THIS AFTERNOON AND THEN CONTINUE TO DEVELOP PROGRESSIVELY SWD THRU
THE CAROLINAS. WITH MLCAPES CLIMBING TO AROUND 2000 J/KG S OF
FRONT...AND 50-60KT OF DEEP LAYER SHEAR IN PRIMARILY UNIDIRECTIONAL
FLOW...STORM MODE EXPECTED TO EVOLVE INTO SHORT LINE SEGMENTS/BOWS.
WIND DAMAGE AND LARGE HAIL WILL BE THE PRIMARY THREAT. HAVE
INCREASED THE WIND DAMAGE CONCERN INTO THE ERN CAROLINAS FOR LATER
THIS AFTERNOON WHERE POTENTIAL SHOULD BE MAXIMIZED IN AREA OF
GREATEST INSTABILITY.
TORNADOS WILL ALSO BE POSSIBLE ASSOCIATED WITH EMBEDDED CIRCULATIONS
IN THE LINEAR SEGMENTS AND ANY SUPERCELL THAT IS ABLE TO DEVELOP IN
THE WARM SECTOR.
WITH HEATING THE SHEAR AND INSTABILITY WILL SUPPORT A SEVERE THREAT
LATER THIS AFTERNOON EXTENDING WWD TO S OF COLD FRONT ACROSS
NRN/CENTRAL GA INTO AL. AGAIN STEEP LAPSE RATES AND MLCAPES TO 2000
J/KG SUPPORTS LARGE HAIL AND DAMAGING WIND POTENTIAL...HOWEVER
SEVERE COVERAGE SHOULD BE A LITTLE LESS GIVEN THE WEAKER DEEP LAYER
UNIDIRECTIONAL SHEAR.
...HIGH PLAINS...
HERE TOO...A STEEP LAPSE RATE ENVIRONMENT WILL EXIST INVOF
STRENGTHENING LEE TROUGH. MOISTURE WILL REMAIN SOMEWHAT
LIMITED...BUT BOUNDARY LAYER DEWPOINTS IN THE 40S WILL CONTRIBUTE TO
MLCAPES OF 500-800 J/KG. FORECAST SOUNDINGS INDICATE THAT AIR MASS
WILL LARGELY REMAIN CAPPED...THOUGH ISOLATED STORMS ARE POSSIBLE
LATER THIS AFTERNOON INTO EVENING WHERE ENHANCED ZONES OF
CONVERGENCE/ASCENT CAN LOCALLY OVERCOME ANY EXISTING CONVECTIVE
INHIBITION. VERTICAL SHEAR PROFILES WILL EXHIBIT STRONG VEERING
WITH HEIGHT WITH 30-45 KT OF DEEP-LAYER SHEAR. THUS...ANY STORMS
THAT CAN DEVELOP AND BECOME SUSTAINED WILL LIKELY EXHIBIT SOME
MIDLEVEL ROTATION WITH THE POTENTIAL FOR HAIL AND STRONG WIND GUSTS.
...NRN INTERMOUNTAIN REGION...
ADVERTISED IMPRESSIVE DIGGING OF TROUGH INTO THE WRN U.S. BEGINS
TODAY. STRONG COLD FRONT MOVES EWD ACROSS WA/OR INTO WRN MT/ID LATER
THIS AFTERNOON.
A STEEP LAPSE ENVIRONMENT WILL EXIST INVOF SURFACE FRONT TODAY WITH
SUFFICIENT MOISTURE PRESENT /PW VALUES AOA .5 INCH/ TO SUPPORT WEAK
INSTABILITY. THE FRONT...OROGRAPHIC FORCING AND THE LEADING EDGE OF
STRONGER HEIGHT FALLS ASSOCIATED WITH UPPER TROUGH APPROACHING THE
REGION SHOULD CONTRIBUTE TO AN INCREASE IN TSTM DEVELOPMENT THROUGH
THE DIURNAL HEATING CYCLE. FORECAST SOUNDINGS INDICATE THE PRESENCE
OF A DEEPLY MIXED BOUNDARY LAYER WHICH SHOULD PROMOTE VIGOROUS
DOWNDRAFT DEVELOPMENT WITH ANY MORE ROBUST CONVECTION.
OTHERWISE...THE MORE INTENSE STORMS WILL BE CAPABLE OF MARGINALLY
SEVERE HAIL.
..HALES/LEVIT.. 05/20/2008
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