Tuesday, April 17, 2007

DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 170900
SWOD48
SPC AC 170859

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT TUE APR 17 2007

VALID 201200Z - 251200Z

..DISCUSSION...
LONG-RANGE MODELS REMAIN CONSISTENT IN BRINGING A
STRONG/NEGATIVELY-TILTED UPPER TROUGH INTO THE PLAINS STATES ON OR
AROUND DAY 5 /SAT. APR. 21/...WHERE A LARGE/UNSTABLE WARM SECTOR
SHOULD BE IN PLACE.

MODELS HAVE BEGUN TO DIFFER THOUGH WITH RESPECT TO TIMING OF THE
TROUGH -- PARTICULARLY BEYOND DAY 5. THE ECMWF DEPICTS A STRONGER
DOWNSTREAM RIDGE OVER THE CENTRAL AND ERN CONUS LEADING UP TO DAY
5...AND THUS IS SLOWER WITH THE EWD PROGRESSION OF -- AND FURTHER N
WITH THE EVENTUAL EJECTION OF -- THIS FEATURE. MEANWHILE...THE GFS
IS FASTER/MORE PROGRESSIVE WITH THE TROUGH...AS IT IMPINGES ON A
WEAKER CENTRAL U.S. RIDGE.

WHILE THE GFS WOULD SUGGEST THAT A SEVERE THREAT MAY DEVELOP OVER
PARTS OF KS/OK/THE TX AND OK PANHANDLES ON DAY 4 -- FOLLOWED BY WHAT
SHOULD BE A FAIRLY WIDESPREAD/SIGNIFICANT EVENT DAY 5...THE SLOWER
ECMWF WOULD SUGGEST THAT THE MAIN EVENT WOULD OCCUR DAY 5...AND
POSSIBLY COULD LINGER INTO DAY 6 FURTHER E/NE.

ATTM...WILL MAINTAIN A DAY 5 OUTLOOK AREA -- THOUGH UNCERTAINTY
PRECLUDES CARRYING A DAY 4 AREA OVER THE WRN PLAINS...OR A DAY 6
AREA INTO THE ERN PLAINS/MID AND UPPER MS VALLEY.

AFTER DAYS 5-6...MODEL DIVERGENCE BECOMES MORE PRONOUNCED. WHILE
BOTH MODELS BRING A SECOND/VERY STRONG TROUGH INTO THE CENTRAL U.S.
IN THE DAY 7-8 TIME FRAME...THE LOCATION/TIMING/INTENSITY OF THE
FEATURE VARIES SIGNIFICANTLY BETWEEN THE TWO MODELS.
THEREFORE...DESPITE WHAT APPEARS TO BE A SECOND SEVERE EVENT
POSSIBLE FOR EARLY NEXT WEEK...PREDICTABILITY DURING THIS TIME FRAME
IS TOO LOW TO WARRANT THE INCLUSION OF A DAY 7/8 OUTLOOK.

.GOSS.. 04/17/2007

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