SWODY2
SPC AC 271728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1128 AM CST THU NOV 27 2008
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...GULF COAST STATES...
AN UPPER-LEVEL LOW OVER THE FOUR CORNERS REGION TONIGHT IS FORECAST
TO OPEN AND MOVE EWD INTO THE PLAINS STATES FRIDAY. AHEAD OF THIS
FEATURE...ZONAL FLOW WILL EXIST ACROSS THE GULF COAST STATES. AT THE
SFC...A COLD FRONT WILL ADVANCE SEWD ACROSS THE SRN PLAINS WITH A
QUASI-STATIONARY FRONT LOCATED ACROSS THE LOWER MS AND SRN TN
VALLEYS. SOUTH OF THE BOUNDARY...ONSHORE FLOW WILL CONTINUE AS THE
UPPER-LEVEL SYSTEM APPROACHES SPREADING 60+ F SFC DEWPOINTS FROM SRN
LA EWD ACROSS SRN MS...SRN AL INTO SRN GA BY FRIDAY AFTERNOON. THIS
SHOULD RESULT IN GRADUAL DESTABILIZATION ACROSS THE WARM SECTOR
DURING THE DAY ESPECIALLY AWAY FROM ANY ONGOING CONVECTION. MODEL
FORECASTS MAINTAIN A 25 TO 35 KT LOW-LEVEL JET ACROSS THE REGION.
LIFT ASSOCIATED WITH THE NRN EDGE OF THE LOW-LEVEL JET SHOULD RESULT
IN NUMEROUS THUNDERSTORMS ALONG THE BOUNDARY FRIDAY MORNING WITH THE
ACTIVITY EXPANDING IN COVERAGE BY AFTERNOON.
CONCERNING THE SEVERE POTENTIAL...FORECAST SOUNDINGS BY MIDDAY
FRIDAY SUGGEST 0-6 KM SHEAR VALUES ACROSS THE REGION WILL BE IN THE
40 TO 55 KT RANGE MOSTLY DUE TO THE WLY FLOW ALOFT. THE SHEAR SHOULD
BE MAINTAINED AND MAY INCREASE SOME DURING THE AFTERNOON AS A 65 TO
75 KT MID-LEVEL JET APPROACHES FROM THE WEST. THE AMOUNT OF VERTICAL
SHEAR MAY BE SUFFICIENT FOR ISOLATED SEVERE STORMS IN AREAS WHERE
INSTABILITY BECOMES MAXIMIZED FRIDAY AFTERNOON. HOWEVER...THERE ARE
STILL QUESTIONS ABOUT HOW MUCH INSTABILITY WILL DEVELOP DUE TO THE
WEAKNESS IN LAPSE RATES. THE ONE POSITIVE IS THE LOW-LEVEL SHEAR.
FORECAST SOUNDINGS AT 18 TO 21Z ALSO SHOW VEERED LOW-LEVEL PROFILES
WITH UNDIRECTIONAL WINDS ABOVE ABOUT 900 MB. THIS MAY SUPPORT A
MARGINAL WIND DAMAGE THREAT. IN ADDITION...A MARGINAL TORNADO THREAT
MAY EXIST ACROSS THE LOWER MS VALLEY...ESPECIALLY SRN LA...WHERE THE
LOW-LEVEL JET SHOULD BE MORE FOCUSED AND FORECAST SOUNDINGS SHOW
ABUNDANT LOW-LEVEL MOISTURE IN THE BOUNDARY LAYER THROUGH ABOUT 850
MB. ALTHOUGH A MARGINAL SEVERE THREAT MAY CONTINUE IN SOME AREAS
OVERNIGHT DUE TO MOISTURE ADVECTION...STRONG VERTICAL SHEAR AND
INCREASING LIFT AHEAD OF THE APPROACHING UPPER-LEVEL TROUGH...THE
THREAT SHOULD BE MORE LOCALIZED DUE TO DECREASING INSTABILITY.
..BROYLES.. 11/27/2008
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