SWODY1
SPC AC 250550
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1150 PM CST SAT NOV 24 2007
VALID 251200Z - 261200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER MS
VALLEY INTO THE CENTRAL GULF COAST STATES...
..SYNOPSIS...
POSITIVELY-TILTED...STRONG UPPER LOW/TROUGH...INITIALLY LOCATED OVER
THE TX BIG BEND REGION AT 12Z TODAY...IS EXPECTED TO BECOME MORE
NEUTRALLY ORIENTED AS IT TRACKS NEWD TOWARD ERN OK/AR THIS FORECAST
PERIOD. IN THE LOW LEVELS...SURFACE LOW EXPECTED TO BE LOCATED
ALONG OR JUST OFF THE UPPER TX/SW LA COAST WILL MOVE NNEWD REACHING
NERN LA BY THIS EVENING /26/00Z/...AND THEN TRACK MORE QUICKLY NNEWD
INTO WRN KY BY 12Z MONDAY. TRAILING COLD FRONT IS EXPECTED TO MOVE
EWD THROUGH THE LOWER MS VALLEY TODAY AND SHOULD REACH THE MS/AL
BORDER AREA BY END OF FORECAST PERIOD. MEANWHILE...SURFACE RIDGE
EXTENDING FROM THE MID ATLANTIC REGION INTO THE SRN APPALACHIANS
WILL BE SLOW TO WEAKEN...AND THUS INHIBIT WARM SECTOR FROM MAKING
MUCH INLAND MOVEMENT ACROSS THE CENTRAL GULF COAST.
..LOWER MS VALLEY AND CENTRAL GULF COAST STATES...
SLY LLJ WILL STRENGTHEN TODAY ACROSS THE LOWER MS VALLEY IN RESPONSE
TO THE APPROACHING TX BIG BEND UPPER LOW. THIS WILL ALLOW LOW LEVEL
MOISTURE TO RETURN NWD AHEAD OF THE COLD FRONT WITH SURFACE
DEWPOINTS IN THE 60S SPREADING INLAND ACROSS LA INTO CENTRAL MS AND
MUCH OF SWRN/WRN AL. LIMITED SURFACE HEATING TODAY AND WEAK LAPSE
RATES WILL RESULT IN MARGINAL INSTABILITY ACROSS MUCH OF THE SLIGHT
RISK AREA. THE EXCEPTION WILL BE ACROSS SRN LA INTO SERN MS/FAR
SWRN AL WHERE SURFACE DEWPOINTS IN THE UPPER 60S WILL CONTRIBUTE TO
MUCAPE VALUES OF 1000-1500 J/KG.
AT 12Z TODAY...TSTMS /MOSTLY ELEVATED/ ARE EXPECTED TO BE ONGOING
WITHIN STRONG WAA REGIME FROM THE ARKLATEX REGION TO THE MIDDLE AND
UPPER TX COAST...WITH SURFACE BASED ACTIVITY OVER THE NWRN GULF IN
THE VICINITY OF THE SURFACE LOW AND WARM FRONT. THE POTENTIAL FOR
SURFACE BASED TSTMS OVER INLAND AREAS OF THE LOWER MS VALLEY IS
EXPECTED TO BECOME PROGRESSIVELY MORE LIKELY WITH TIME AS THE WARM
SECTOR EXPANDS N/NEWD IN ADVANCE OF THE COLD FRONT. LATEST MODEL
DATA WOULD SUGGEST THAT THE WARM SECTOR SHOULD SPREAD INLAND ACROSS
MUCH OF SRN LA AND INTO PARTS OF SRN MS TO FAR SWRN AL.
FORECAST SOUNDINGS WITHIN WARM SECTOR INDICATE THAT BOTH LOW-LEVEL
AND DEEP-LAYER SHEAR WILL INCREASE THROUGH THE PERIOD WITH KINEMATIC
ENVIRONMENT BECOMING INCREASINGLY SUPPORTIVE OF EMBEDDED BOW ECHOES
AND SUPERCELLS BY THIS AFTERNOON AND CAPABLE OF PRODUCING MAINLY
DAMAGING WINDS AND A FEW TORNADOES.
AS INDICATED IN EARLIER OUTLOOKS...GREATEST TORNADO THREAT IS
EXPECTED TO BE GENERALLY ALONG AND S OF I-20 ACROSS SOUTH CENTRAL/
SERN LA INTO SRN MS WHERE A MOIST...UNSTABLE BOUNDARY LAYER WILL
COEXIST WITH INCREASING LOW LEVEL SHEAR. DEEP LAYER ASCENT
SPREADING EWD WILL MAINTAIN A SEVERE WEATHER THREAT TONIGHT INTO
MONDAY MORNING IN ASSOCIATION WITH PRE-FRONTAL CONVECTIVE BAND
MOVING THROUGH MS/SERN LA INTO WRN AL. THE TORNADO THREAT IS
EXPECTED TO BE CONFINED TO SERN MS/SWRN AL DURING THE OVERNIGHT
PERIOD WHERE LOW LEVEL SHEAR SHOULD BE GREATEST IN VICINITY OF WARM
FRONT.
.PETERS/CROSBIE.. 11/25/2007
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