SWODY1
SPC AC 200539
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT TUE MAY 20 2008
VALID 201200Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN VA AND THE CAROLINAS
WWD INTO AL...
...SYNOPSIS...
LARGE-SCALE OMEGA BLOCK WILL BE MAINTAINED OVER THE CONUS THROUGH
THE DAY ONE PERIOD. IN THE E...SEVERAL VORTICITY MAXIMA WILL ROTATE
AROUND DEEP VORTEX CENTERED OVER ONTARIO/QUEBEC...THE MOST NOTABLE
OF WHICH WILL TRANSLATE FROM THE MID/UPPER OH VALLEY ENEWD ACROSS
THE MIDDLE ATLANTIC COAST. IN THE W...SHORT WAVE TROUGH OVER THE
FAR ERN PACIFIC WILL MOVE ONSHORE TODAY...SUPPORTING AN
AMPLIFICATION TO LARGER-SCALE TROUGH ALONG THE WEST COAST.
IN THE LOW LEVELS...SURFACE LOW ASSOCIATED WITH THE OH VALLEY SHORT
WAVE TROUGH IS FORECAST TO DEVELOP FROM WV EWD TO OFF THE MID
ATLANTIC COAST BY AFTERNOON. TRAILING FOLD FRONT WILL PUSH SWD
THROUGH THE TN VALLEY AND SRN APPALACHIANS AND INTO THE GULF COAST
STATES. THIS FRONT WILL BE THE PRIMARY FOCUS FOR SEVERE TSTM
DEVELOPMENT TODAY INTO TONIGHT.
ELSEWHERE...PACIFIC COLD FRONT WILL PROGRESS EWD FROM THE PACIFIC NW
INTO THE NRN INTERMOUNTAIN REGION WITH SRN EXTENSION OF BOUNDARY
MOVING MORE SEWD INTO THE LOWER CO VALLEY. FINALLY...A LEE TROUGH
WILL STRENGTHEN THROUGH THE PERIOD OVER THE HIGH PLAINS REGION.
...TIDEWATER AREA SWWD INTO THE CNTRL GULF STATES...
CURRENT SURFACE OBSERVATION AND GOES IPW SOUNDER DATA INDICATE THAT
BOUNDARY LAYER MOISTENING IS OCCURRING ACROSS THE GULF STATES WITH
DEWPOINTS INCREASING THROUGH THE 50S TO LOWER/MID 60S ALONG THE
IMMEDIATE COAST. THIS MOISTURE COUPLED WITH EWD EXTENSION OF STEEP
MIDLEVEL LAPSE RATE /EML/ PLUME ORIGINATING OVER THE ROCKIES AND
HIGH PLAINS WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS THIS
AFTERNOON WITH MLCAPES APPROACHING 1000-1500 J/KG.
CLUSTERS OF TSTMS /LIKELY SLIGHTLY ELEVATED/ ARE EXPECTED TO BE
ONGOING AT THE ONSET OF THE FORECAST OVER PORTIONS OF WV/VA. THIS
ACTIVITY SHOULD QUICKLY MOVE EWD THIS MORNING IN CONCERT WITH SHORT
WAVE TROUGH AND SURFACE LOW WITH SOME THREAT OF MARGINALLY SEVERE
HAIL. THEREAFTER...CONVERGENCE ALONG FRONT...DAYTIME HEATING AND
TRAILING FRINGE OF STRONGER HEIGHT FALLS ATTENDANT TO PASSING
MIDLEVEL WAVE ALL WILL CONTRIBUTE TO AN INCREASE IN STORM COVERAGE
AND INTENSITY THIS AFTERNOON FROM SERN VA/ERN NC SWWD INTO NRN GA
AND PERHAPS AL.
FORECAST SOUNDINGS INDICATE LARGELY STRAIGHT HODOGRAPHS WITH 40-50
KT OF DEEP LAYER SHEAR. AS SUCH...THE POTENTIAL WILL EXIST FOR
SPLITTING SUPERCELLS IN ADDITION TO MORE LINEAR...POSSIBLY BOWING
STRUCTURES. LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY
SEVERE WEATHER THREATS WITH THE MOST INTENSE STORMS. THE GREATEST
THREAT FOR A TORNADO OR TWO WILL EXIST WITH ANY SUPERCELLS THAT CAN
DEVELOP OVER SERN VA INTO THE ERN CAROLINAS WHERE STRONGER LOW-LEVEL
WILL BE MAINTAINED.
...NRN INTERMOUNTAIN REGION...
A STEEP LAPSE ENVIRONMENT WILL EXIST INVOF SURFACE FRONT TODAY WITH
SUFFICIENT MOISTURE PRESENT /PW VALUES AOA .5 INCH/ TO SUPPORT WEAK
CONVECTIVE INSTABILITY. THE FRONT...OROGRAPHIC FORCING AND THE
LEADING EDGE OF STRONGER HEIGHT FALLS ASSOCIATED WITH UPPER TROUGH
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.
...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.
..MEAD/CROSBIE.. 05/20/2008
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