SWODY1
SPC AC 201237
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0737 AM CDT TUE MAY 20 2008
VALID 201300Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN VA/CAROLINAS SWWD
ACROSS THE SRN APPALACHIANS TOWARDS THE LOWER MS RIVER VALLEY...
...TIDEWATER AREA SWWD INTO THE CNTRL GULF STATES...
CURRENT SURFACE OBSERVATION INDICATE THAT BOUNDARY LAYER MOISTENING
IS OCCURRING ACROSS THE GULF STATES/SOUTHEAST WITH DEWPOINTS
INCREASING THROUGH THE 50S TO LOWER/MID 60S. 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
1000-2000 J/KG. 12Z SOUNDINGS FROM FFC/CHS/MHX ALL INDICATE MID
LEVEL LAPSE RATES GREATER THAN 7.5 C/KM...SUGGESTING SEVERE THREAT
MAY BE A BIT GREATER THAN EARLIER FORECAST FROM SERN NC ACROSS NRN
GA WHERE STRONG HEATING WILL OCCUR.
CLUSTERS OF WEAK...ELEVATED TSTMS WILL QUICKLY MOVE EWD THIS MORNING
IN CONCERT WITH SHORT WAVE TROUGH AND SURFACE LOW.
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/AL AND PERHAPS
ERN MS.
FORECAST SOUNDINGS MAINTAIN 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 AS MORE ROBUST CONVECTION DEVELOPS DURING THE MID
AFTERNOON. LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY SEVERE
WEATHER THREATS WITH THE MOST INTENSE STORMS...INCLUDING SOME VERY
LARGE HAIL EVENTS GIVEN LARGE MID LEVEL LAPSE RATES AND LIKELIHOOD
OF ROTATING STORMS. IN ADDITION...RIGHT MOVERS WILL POSE A THREAT
OF ISOLATED TORNADOES GIVEN DEGREE OF LOW LEVEL SHEAR FORECAST OVER
THE REGION. SEVERE THREAT WILL MOVE OFF THE CAROLINA COAST DURING
THE EVENING...WHILE THREAT DIMINISHES WITH LOSS OF HEATING WWD
TOWARDS THE LOWER MS RIVER VALLEY.
...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
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.
...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.
..EVANS/MEAD/CROSBIE.. 05/20/2008
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