SWODY1
SPC AC 220049
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0649 PM CST WED NOV 21 2007
VALID 220100Z - 221200Z
..THERE IS A SLGT RISK OF SVR TSTMS TONIGHT ACROSS PARTS OF THE LWR
MS VALLEY/CNTRL GULF STATES....
..SYNOPSIS...
A SIGNIFICANT COLD INTRUSION IS ONGOING TO THE LEE OF THE ROCKIES IN
ASSOCIATION WITH THE AMPLIFICATION OF A POLAR TROUGH ACROSS THE
NORTH CENTRAL STATES. THE SURFACE FRONT IS NOW RAPIDLY ADVANCING
TOWARD THE WESTERN GULF COAST/LOWER MISSISSIPPI VALLEY...WELL TO THE
SOUTH OF THE POLAR STREAM. AND...THE INITIAL PRIMARY SHORT WAVE
IMPULSE WITHIN THE BROADER SCALE UPPER TROUGH IS PROGGED TO LIFT
EAST NORTHEAST OF THE LOWER MISSOURI VALLEY...TOWARD THE LOWER GREAT
LAKES REGION...THROUGH THE REMAINDER OF THE FORECAST PERIOD.
..OHIO/TENNESSEE VALLEYS...
MODELS SUGGEST THAT THE STRONGER LOW-LEVEL FLOW FIELDS WILL SHIFT
NORTHEASTWARD THROUGH THE OHIO VALLEY TONIGHT...BUT SURFACE WAVE
DEVELOPMENT ALONG FRONTAL ZONE IS EXPECTED TO REMAIN FAIRLY WEAK.
THIS...IN CONJUNCTION WITH WEAK DESTABILIZATION...PRIMARILY DUE TO
WEAK WARM SECTOR LAPSE RATES...IS EXPECTED TO MINIMIZE ADDITIONAL
SEVERE POTENTIAL LATER TONIGHT ACROSS MOST AREAS NORTH OF THE GULF
STATES.
ONGOING STORMS NEAR FRONT TRAILING TO THE SOUTH OF SURFACE LOW MAY
REMAIN STRONG/SEVERE ACROSS PARTS OF WESTERN KENTUCKY/TENNESSEE
THROUGH THE 02-04Z TIME FRAME. THIS IS WHERE BETTER BOUNDARY LAYER
HEATING OCCURRED TODAY. BUT...WITH THE ONSET OF DIURNAL COOLING AND
FRONTAL PROGRESSION THROUGH THE INSTABILITY AXIS...WEAKENING STORM
TRENDS ARE ANTICIPATED WITH EASTWARD PROGRESSION ACROSS THE MID
SOUTH.
..LOWER MISSISSIPPI VALLEY/CNTRL INTO ERN GULF STATES...
OTHERWISE...THE PRIMARY CONVECTIVE THREAT THROUGH THE OVERNIGHT
HOURS MAY ACCOMPANY A PRE-FRONTAL CONVECTIVE CLUSTER WHICH IS NOW
ONGOING AND SPREADING INTO/THROUGH THE LOWER MISSISSIPPI VALLEY. A
ZONE OF ENHANCED LIFT BETWEEN INTERACTING POLAR AND SUBTROPICAL
STREAMS APPEARS TO BE SUPPORTING THIS ACTIVITY...WHICH SEEMS LIKELY
TO PERSIST AS FORCING DEVELOPS EASTWARD WITHIN A MOIST AND UNSTABLE
AIR MASS...WITH CAPE ON THE ORDER OF 1000 J/KG...ACROSS SOUTHERN
LOUISIANA/SOUTHERN MISSISSIPPI. 30-40 KT WESTERLY MEAN FLOW
FIELDS...AND PERHAPS EVAPORATIVE COOLING ASSOCIATED WITH AN
UNSATURATED MID-LEVEL ENVIRONMENT...MAY CONTRIBUTE TO THE POTENTIAL
FOR STRONG GUSTY WINDS AND HAIL WITH THE STORM CLUSTER. THIS SEVERE
THREAT MAY LINGER THROUGH LATE TONIGHT/EARLY THURSDAY ...BEFORE
ACTIVITY WEAKENS IN A LESS UNSTABLE AIR MASS ACROSS THE WESTERN
FLORIDA PANHANDLE/SOUTHERN ALABAMA.
.KERR.. 11/22/2007
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