DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 200824
SWOD48
SPC AC 200823

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0323 AM CDT TUE MAY 20 2008

VALID 231200Z - 281200Z

...DISCUSSION...
MODELS CONTINUE TO DIVERGE IN TIMING OF THE BREAKDOWN OF THE CENTRAL
U.S. RIDGE...WITH THE FASTER ECMWF DRIVING A STRONG COLD FRONT SEWD
ACROSS THE PLAINS BEGINNING LATE IN THE DAY 5 PERIOD /SATURDAY MAY
25/. THE GFS IS SOMEWHAT WEAKER -- AND ABOUT 18 HOURS SLOWER --
WITH THIS FRONT.

MODELS AGREE IN THE DAY 4-5 TIME FRAME...HOWEVER...THAT A VERY
WARM/MOIST BOUNDARY LAYER WILL REMAIN IN PLACE BENEATH STEEP
MID-LEVEL LAPSE RATES AND STRONG SSWLY MID LEVEL FLOW.
THEREFORE...SEVERE THREAT WILL PERSIST ALONG ERN FRINGES OF THE
LARGE-SCALE WRN U.S. TROUGH. PRIMARY THREAT DAY 4 SHOULD REMAIN
GENERALLY ACROSS THE HIGH PLAINS...FROM WRN OK AND THE TX/OK
PANHANDLE REGION NWD INTO THE WRN DAKOTAS. MODELS -- PARTICULARLY
THE ECMWF -- THEN SUGGEST THAT THE SEVERE POTENTIAL SHOULD EXPAND A
BIT FURTHER E INTO THE NRN AND CENTRAL PLAINS DAY 5.

WHILE A SEVERE THREAT WILL LIKELY CONTINUE INTO DAY 6 AND BEYOND AS
A COLD FRONT MOVES SEWD ACROSS THE PLAINS AND IMPINGES ON
WARM/MOIST/UNSTABLE AIRMASS IN PLACE...MODEL DIVERGENCE WITH RESPECT
TO TIMING OF THE FRONT PRECLUDES THE ISSUANCE OF ANY AREAS BEYOND
DAY 5 ATTM.

..GOSS.. 05/20/2008

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