DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 141008
SWOD48
SPC AC 141008

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0408 AM CST THU FEB 14 2008

VALID 171200Z - 221200Z

..SVR STORMS POSSIBLE ACROSS ERN GULF/S ATLC COAST STATES SUN...

MEDIUM RANGE FORECAST GUIDANCE INDICATES THAT THE SOUTHERN BRANCH
IMPULSE...EMANATING FROM THE MEXICAN PLATEAU...WILL FINALLY PHASE
WITH THE NORTHERN BRANCH SHORT WAVE TROUGH DIGGING TO THE SOUTHEAST
OF THE NORTH CENTRAL STATES ON SUNDAY. AND...THIS IS EXPECTED TO
CONTRIBUTE TO THE EVOLUTION OF A HIGH AMPLITUDE/INCREASINGLY
NEGATIVE TILTED BROADER SCALE TROUGH NEAR/EAST OF THE MISSISSIPPI
VALLEY. AS THIS OCCURS...STRONG SURFACE CYCLOGENESIS IS EXPECTED TO
PROCEED. ALTHOUGH THERE IS SOME CONCERN THAT MODELS MAY BE A BIT
TOO FAR TO THE WEST WITH THE TRACK OF THIS LOW...IT NOW APPEARS
PROBABLE THAT IT WILL BE TO THE WEST OF THE APPALACHIANS.

THROUGH SUNDAY EVENING...A MOIST AND AT LEAST WEAKLY UNSTABLE WARM
SECTOR IS EXPECTED TO BE CONFINED TO THE EASTERN GULF STATES...
WHERE STRENGTHENING DEEP LAYER AND LOW LEVEL SHEAR PROFILES AHEAD OF
THE BASE OF THE UPPER TROUGH WILL SUPPORT A RISK FOR SEVERE
THUNDERSTORM...WITH POTENTIAL FOR TORNADOES. THERE ARE INCREASING
POSITIVE INDICATIONS THAT MOISTENING OFF THE WESTERN ATLANTIC MAY
BECOME SUFFICIENT TO MAINTAIN A SEVERE THREAT ACROSS THE SOUTH
ATLANTIC COAST STATES SUNDAY NIGHT INTO EARLY MONDAY.

THEREAFTER...MODELS INDICATE THE BEGINNINGS OF A PATTERN CHANGE. AS
THE UPPER TROUGH LIFTS OUT OF THE EASTERN STATES DURING THE EARLY TO
MIDDLE PARTS OF NEXT WEEK...A STRENGTHENING MORE ZONAL FLOW REGIME
IS PROGGED TO SET UP ACROSS THE EAST CENTRAL PACIFIC INTO THE
SOUTHWESTERN STATES. AND...SIGNIFICANT MOISTENING/ DESTABILIZATION
AND INLAND RETURN FLOW APPEARS LIKELY TO OCCUR THROUGH THE SOUTHERN
PLAINS/LOWER MISSISSIPPI VALLEY REGION BY MID WEEK...POSSIBLY
ACCOMPANIED BY AN INCREASING SEVERE THREAT. HOWEVER...THIS WILL
LARGELY DEPEND ON TIMING OF SIGNIFICANT IMPULSES EMANATING FROM THE
UPSTREAM JET...WHICH IS STILL HIGHLY UNCERTAIN.

.KERR.. 02/14/2008

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