SWODY1
SPC AC 211236
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0736 AM CDT THU AUG 21 2008
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
FROM SRN/CENTRAL MT TO CENTRAL ND...
...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT OVER NE FL AND
SE GA...
...MT/ND AREA THIS AFTERNOON INTO TONIGHT...
SOME ELEVATED CONVECTION PERSISTS THIS MORNING OVER WRN ND/E CENTRAL
MT IN ASSOCIATION WITH A WEAK LEAD SHORTWAVE TROUGH EJECTING NEWD.
THIS MID LEVEL WAVE IS ACCOMPANIED BY A SURFACE TROUGH FROM NW SD
INTO WRN ND. BOUNDARY LAYER DEWPOINTS AROUND 60 F WILL BE
MAINTAINED TODAY E OF THE SURFACE TROUGH...WHILE STRONG SURFACE
HEATING IS EXPECTED NEAR AND W OF THE BOUNDARY. THIS SURFACE
HEATING/MIXING WILL HELP REDUCE CONVECTIVE INHIBITION BY MID-LATE
AFTERNOON ALONG THE SURFACE TROUGH...WHERE WIDELY SCATTERED
THUNDERSTORMS MAY FORM. THE COMBINATION OF MLCAPE VALUES NEAR 1500
J/KG AND EFFECTIVE BULK SHEAR AROUND 35 KT WILL SUPPORT ORGANIZED
CLUSTERS AND SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING
GUSTS.
LOW-LEVEL MOISTURE WILL BE MUCH MORE LIMITED FARTHER W INTO
CENTRAL/ERN MT...W OF THE SURFACE TROUGH. HOWEVER...VERY STEEP
LOW-LEVEL LAPSE RATES WILL DEVELOP OVER THIS AREA WITH DAYTIME
HEATING. THE APPROACH OF A STRONG MID LEVEL TROUGH AND FRONTAL
SURGE FROM THE W WILL LIKELY SUPPORT HIGH-BASED THUNDERSTORM
DEVELOPMENT THIS AFTERNOON ACROSS CENTRAL/S CENTRAL MT...WITH
CONVECTION EXPECTED TO SPREAD EWD/ENEWD TOWARD WRN ND BY EARLY
TONIGHT. DESPITE WEAK INSTABILITY /MUCAPE LESS THAN 500 J/KG/...THE
STEEP LAPSE RATES AND STRENGTHENING MID LEVEL FLOW WILL RESULT IN AN
ENVIRONMENT SUPPORTIVE OF THUNDERSTORMS WITH DAMAGING OUTFLOW GUSTS
THIS AFTERNOON INTO EARLY TONIGHT. SOME OF THIS CONVECTION COULD
SURVIVE AND INTERACT WITH THE INITIAL SURFACE BOUNDARY IN
ND...MAINTAINING A THREAT FOR AT LEAST ISOLATED LARGE HAIL/DAMAGING
WINDS INTO LATE TONIGHT ACROSS CENTRAL ND.
...NE FL/SE GA THROUGH TONIGHT...
TROPICAL STORM FAY WILL DRIFT WWD OVER N FL THROUGH TONIGHT /SEE
LATEST NHC ADVISORIES FOR DETAILS/. VERY GRADUAL WEAKENING OF THE
STORM IS EXPECTED AS IT REMAINS INLAND FOR MUCH OF THE FORECAST
PERIOD...THUS LOW-MID LEVEL WINDS AND ASSOCIATED SHEAR WILL ALSO
WEAKEN SLOWLY WITH TIME. HOWEVER...WWD MOVEMENT OF THE CYCLONE WILL
BRING THE ZONE OF STRONGER LOW-LEVEL SHEAR/INSTABILITY AND OUTER
BAND CELLULAR CONVECTION INLAND OVER NE FL/SE GA THROUGH TONIGHT.
THEREFORE...WILL MAINTAIN A SLIGHT RISK AREA FOR RAINBAND SUPERCELLS
AND A COUPLE OF TORNADOES LATER TODAY INTO TONIGHT.
..THOMPSON/GRAMS.. 08/21/2008
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