DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 240826
SWOD48
SPC AC 240826

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0226 AM CST TUE FEB 24 2009

VALID 271200Z - 041200Z

...DISCUSSION...
MODELS CONTINUE TO FORECAST FAIRLY PROGRESSIVE FLOW PATTERN ACROSS
THE CONUS INTO THE WEEKEND...WITH EVENTUAL EVOLUTION INTO A LONGWAVE
TROUGH OVER THE EAST COAST AND LARGE RIDGE ACROSS MUCH OF THE
ROCKIES/INTERMOUNTAIN WEST BY EARLY NEXT WEEK.

...DAY 4...
FAST MOVING/LOW-AMPLITUDE SHORTWAVE TROUGH WILL EJECT QUICKLY NEWD
FRIDAY OUT OF THE OH VALLEY AND INTO THE NORTHEAST/QUEBEC...WITH
BOTH ECMWF AND OPERATION GFS MOVING STRONG SURFACE COLD FRONT EWD TO
ALONG THE ERN SEABOARD FRIDAY AFTERNOON/EVENING. LOW LEVEL
MOISTURE/HEATING AND RESULTANT INSTABILITY WILL LIKELY BE SCANT
AHEAD OF THIS FRONT AND PRECLUDE MENTION OF SEVERE THUNDERSTORMS
ATTM. ALTHOUGH...STRONG FLOW AND DEEP ASCENT ALONG FRONT MAY
SUPPORT RISK OF DAMAGING WINDS WITH SHALLOW MOIST CONVECTION FROM
THE MID ATLANTIC INTO THE CAROLINAS SHOULD BOUNDARY LAYER
DESTABILIZE.

TAIL END OF SURFACE COLD FRONT IS EXPECTED TO STALL OR SLOW ITS SEWD
MOTION ACROSS THE CENTRAL GULF COAST STATES FRIDAY AFTERNOON. THIS
COULD PROVIDE FOCUS FOR STRONG/SEVERE THUNDERSTORMS AS MODIFIED GULF
MOISTURE INCREASES OUT OF THE G.O.M. AND AREA IS OVERRIDDEN BY 50+
KT WLY H5 WINDS. GIVEN DEGREE OF MODEL DISCREPANCIES...CONFIDENCE
IS NOT HIGH ENOUGH TO WARRANT OUTLOOK ATTM.

...DAY 5-8...
THOUGH BOTH ECMWF AND GFS AGREE IN LONGWAVE DEVELOPMENT ALONG THE
ERN U.S. BY EARLY NEXT WEEK...SUBSTANTIAL DIFFERENCES ARE EVIDENT IN
THE HANDLING OF THE SHORTWAVE TROUGH WHICH WILL HELP CARVE OUT THE
LARGER TROUGH OVER THE WEEKEND. IN ADDITION...MREF INDICATES
SUBSTANTIAL SPREAD IN ITS MEMBERS AT H5 BEYOND 96 HRS. ECMWF IS
MOST AGGRESSIVE WITH THIS TROUGH AND ASSOCIATED SEVERE THREAT
DEVELOPING ALONG THE CENTRAL GULF COAST SATURDAY NIGHT EWD ACROSS
THE SOUTHEASTERN STATES SUNDAY. HOWEVER...GIVEN DISCREPANCIES IN
FORECAST STRENGTH/LOCATION OF TROUGH AND ASSOCIATED SURFACE
LOW/FRONT...PREDICTABILITY REMAINS TOO LOW ATTM TO WARRANT AN
OUTLOOK.

..EVANS.. 02/24/2009

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