SWODY1
SPC AC 252000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT WED APR 25 2007
VALID 252000Z - 261200Z
..THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN/TONIGHT FROM
PARTS OF THE OZARK PLATEAU/LOWER MISSISSIPPI VALLEY EASTWARD TOWARD
THE APPALACHIANS....
..THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN ACROSS PARTS OF
VA....
..SYNOPSIS...
DOWNSTREAM OF A BUILDING UPPER RIDGE OVER THE EASTERN PACIFIC...A
TROUGH IS BEGINNING TO SPLIT INTO SMALLER SCALE IMPULSES AS IT
PROGRESSES INTO THE PACIFIC COAST. ONE IMPULSE IS ADVANCING
EASTWARD TOWARD THE NORTHERN ROCKIES...WHILE ANOTHER DIGS INTO THE
NORTHERN CALIFORNIA COAST. THE LATTER FEATURE IS PROGGED TO
CONTINUE TOWARD THE LOWER COLORADO VALLEY THROUGH THE REMAINDER OF
THIS PERIOD...AS THE FORMER CONTINUES ACROSS AND BEGINS TO DIG TO
THE LEE OF THE NORTHERN ROCKIES. AS THIS OCCURS...A BROAD SOUTHERN
BRANCH CLOSED LOW/TROUGH...NOW SLOWLY ADVANCING TO THE EAST OF THE
CENTRAL/SOUTHERN PLAINS...IS EXPECTED TO BEGIN A NORTHEASTWARD
ACCELERATION. MODELS INDICATE THAT THIS SYSTEM WILL TAKE ON AN
INCREASING NEGATIVE TILT THIS EVENING...AS AN EMBEDDED IMPULSE
PIVOTS AROUND ITS SOUTHERN/EASTERN PERIPHERY. IN RESPONSE...MODELS
STILL APPEAR TO SUGGEST THE REDEVELOPMENT OF A SOUTHERLY LOW-LEVEL
JET OFF THE CENTRAL GULF OF MEXICO...THROUGH PARTS OF
MISSISSIPPI/ALABAMA INTO EASTERN TENNESSEE BY LATE TONIGHT.
..LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST STATES/TENNESSEE...
BOUNDARY LAYER BASED INSTABILITY AHEAD OF ONGOING MESOSCALE
CONVECTIVE SYSTEM IS PRESENTLY WEAK. BUT...WITH FURTHER SURFACE
HEATING THIS AFTERNOON...AND AN INCREASE IN MOISTURE...WHICH WILL
CONTINUE THROUGH TONIGHT...A GRADUAL INTENSIFICATION OF CONVECTION
IS EXPECTED. DEEP LAYER SHEAR BENEATH 50+ KT SOUTH SOUTHWESTERLY
MID-LEVEL FLOW IS STRONG AND ALREADY SUPPORTIVE OF SEVERE POTENTIAL.
SOME UNCERTAINTY EXISTS CONCERNING THE TIMING OF THE STRENGTHENING
OF THE LOW-LEVEL FLOW...BUT ONCE IT DOES... TORNADO/DAMAGING WIND
POTENTIAL WILL INCREASE AS LOW-LEVEL HODOGRAPHS ENLARGE. THIS MAY
OCCUR BY THIS EVENING ACROSS PARTS OF CENTRAL/EASTERN
MISSISSIPPI...WITH RISK CONTINUING AND POSSIBLY INCREASING OVERNIGHT
INTO ALABAMA.
..OZARK PLATEAU...
LATEST RUC ANALYSIS AND SATELLITE IMAGERY SUGGEST THAT A NEW
STRONGER MID-LEVEL CIRCULATION CENTER...WITHIN BROADER SCALE
SOUTHERN BRANCH LOW....HAS DEVELOPED NEAR THE CENTRAL
OKLAHOMA/KANSAS BORDER. THIS IS GENERALLY SOUTH OF THE MID-LEVEL
COLD CORE OF UPPER SYSTEM...BUT ASSOCIATED FORCING IS CONTRIBUTING
TO ONGOING CONVECTIVE DEVELOPMENT ACROSS NORTHEAST OKLAHOMA/
SOUTHEAST KANSAS/WEST CENTRAL MISSOURI. SURFACE HEATING JUST AHEAD
OF COLD FRONT SURGING INTO THE SOUTHERN PLAINS HAS STEEPENED
LOW-LEVEL LAPSE RATES ACROSS MUCH OF THE REMAINDER OF THE OZARK
PLATEAU. THIS IS IN THE WAKE OF AN INITIAL WIND SHIFT/COOL SURGE
..BUT SURFACE DEW POINTS REMAIN IN THE UPPER 50S/NEAR 60F...
SUPPORTING MIXED LAYER CAPE UP TO AROUND 500 J/KG. GIVEN SUFFICIENT
DEEP LAYER SHEAR BENEATH 40 KT CYCLONIC 500 MB FLOW... ISOLATED
SUPERCELLS ARE POSSIBLE LATE THIS AFTERNOON. THIS WILL ENHANCE RISK
OF HAIL IN STRONGER STORMS...AND AN ISOLATED TORNADO SEEMS POSSIBLE
WHERE SURFACE WINDS ARE SOUTHEASTERLY TO THE SOUTHEAST OF SURFACE
CYCLONE...ACROSS PARTS OF NORTHWEST ARKANSAS/ SOUTHWEST MISSOURI.
..WESTERN STATES...
LARGE SCALE FORCING ASSOCIATED WITH EVOLVING UPPER PATTERN WILL
CONTRIBUTE TO DESTABILIZATION AND SCATTERED THUNDERSTORM ACTIVITY
ACROSS PARTS OF THE INTERMOUNTAIN WEST...AS WELL AS ALONG THE SIERRA
NEVADA...WHERE ACTIVITY MAY PERSIST WELL INTO THE EVENING.
AND...INVERTED-V TYPE PROFILES ACROSS THE NORTHERN INTERMOUNTAIN
REGION MAY PROVE FAVORABLE FOR ISOLATED DOWNBURSTS.
..MID ATLANTIC...
WEAK SURFACE LOW/FRONT TO THE LEE OF THE CENTRAL APPALACHIANS MAY
PROVIDE A FOCUS FOR ISOLATED CONVECTIVE DEVELOPMENT LATE THIS
AFTERNOON. IF THIS OCCURS...THE DEEP MIXED BOUNDARY LAYER WITH
LARGE TEMPERATURE/DEW POINT SPREADS...WHICH HAS EVOLVED ACROSS PARTS
OF CENTRAL/EASTERN VIRGINIA..COULD SUPPORT STRONG SURFACE GUSTS.
.KERR.. 04/25/2007
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