DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 210843
SWOD48
SPC AC 210842

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0342 AM CDT WED MAY 21 2008

VALID 241200Z - 291200Z

...DISCUSSION...
GFS AND ECMWF ARE IN GOOD AGREEMENT THIS FORECAST -- PARTICULARLY
THROUGH ABOUT DAY 6 /MON. MAY 26/. MODELS FINALLY AGREE ON THE
TIMING OF THE START OF THE BREAKDOWN OF THE CENTRAL U.S. RIDGE...AS
PIECES OF THE WRN U.S. TROUGH BEGIN EJECTING NEWD INTO THE N CENTRAL
CONUS.

IT APPEARS THAT THIS BREAKDOWN WILL BEGIN DAY 4 /SAT. MAY
24/...WHICH WILL ALLOW A SURFACE FRONT TO BEGIN MOVING SEWD ACROSS
THE PLAINS. THIS FRONT -- WHICH WILL MOVE MORE QUICKLY EWD ACROSS
THE GREAT LAKES AND INTO ERN CANADA ON ITS NRN FRINGE BUT WILL SHIFT
MORE SLOWLY SWD ACROSS THE PLAINS -- SHOULD SEVERE AS A FOCUS FOR
THUNDERSTORM DEVELOPMENT THROUGH AT LEAST THE FIRST HALF OF THE
EXTENDED FORECAST PERIOD. WITH A MOIST BOUNDARY LAYER IN PLACE
ACROSS THE PLAINS SUPPORTIVE OF MODERATE INSTABILITY...AND WITH
MODERATELY-STRONG FLOW SPREADING ACROSS THE N CENTRAL CONUS IN
CONJUNCTION WITH THE UPPER RIDGE BREAKDOWN...SHEAR/INSTABILITY
COMBINATION SHOULD BE SUFFICIENT FOR A MULTIPLE-DAY THREAT FOR
RELATIVELY WIDESPREAD SEVERE STORMS.

LATER IN THE PERIOD THE FRONT SHOULD CONTINUE TO SETTLE SWD WHILE
THE UPPER FLOW SLACKENS SOMEWHAT. THIS COMBINED WITH SOME INCREASE
IN MODEL DISAGREEMENT WITH TIME PRECLUDES THE ISSUANCE OF AN OUTLOOK
AREA DAY 7 OR 8. HOWEVER...SUFFICIENT CONFIDENCE EXISTS THIS
FORECAST TO INCLUDE OUTLOOK AREAS ON DAYS 4-6 IN ANTICIPATION OF
WIDESPREAD CONVECTION AND ASSOCIATED SEVERE POTENTIAL.

..GOSS.. 05/21/2008

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@PO.UIUC.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.