DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 260901
SWOD48
SPC AC 260900

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT TUE MAY 26 2009

VALID 291200Z - 031200Z

...DISCUSSION...
GFS AND ECMWF IN DECENT AGREEMENT THROUGH THE MEDIUM RANGE...WITH
BOTH FORECASTING THE DEPARTURE OF AN ERN U.S. TROUGH DAYS 4-6 /FRI.
TO SUN. MAY 29-31/ TO BE FOLLOWED BY INCREASING/COMPLEX TROUGHING
OVER THE WRN HALF OF THE COUNTRY THROUGH THE REMAINDER OF THE
PERIOD.

OVERALL...THE EVOLUTION OF THIS PATTERN POINTS TO AN INCREASING
SEVERE THREAT ACROSS THE CENTRAL AND NRN PLAINS AND INTO THE UPPER
MIDWEST REGION...AS SEVERAL WEAK FEATURES MOVE THROUGH INITIALLY
NWLY -- AND THEN INCREASINGLY WLY -- MID-LEVEL FLOW PATTERN ACROSS
THIS REGION. BENEATH THIS FLOW FIELD...MOISTURE RETURNING NWD INTO
THE PLAINS SHOULD SUPPORT INCREASINGLY-UNSTABLE CONDITIONS AND
SEVERAL AFTERNOON/EVENING EPISODES OF SEVERE STORMS.

ATTM...MODEST MODEL DIFFERENCES IN TIMING OF THE SUBTLE FEATURES
MOVING THROUGH THE FLOW FIELD MAKE NARROWING DOWN THE GREATER SEVERE
POTENTIAL -- BOTH AREALLY AND TEMPORALLY -- DIFFICULT. IT APPEARS
THAT MOISTURE RETURN NWD DAY 4 /FRI. MAY 29/ MAY BE INSUFFICIENT FOR
A MORE WIDESPREAD THREAT...BUT WILL HIGHLIGHT AN AREA FOR DAY 5
/SAT. MAY 30/ CENTERED OVER THE MID MO VALLEY REGION. HERE...MODELS
SUGGEST THAT A NW-SE WARM FRONT -- MARKING THE LEADING EDGE OF A
RETURNING HIGHER THETA-E AIRMASS -- WILL LIE FROM THE SD/NEB
VICINITY INTO THE IA/MO AREA. POTENTIAL FOR STORMS DEVELOPING INVOF
THE SURFACE FRONT TO EXPAND/ORGANIZE AND SHIFT QUICKLY SEWD WITHIN
FLOW FIELD FEATURING LOW-LEVEL SLYS/SELYS BENEATH 30 TO 50 KT NWLYS
ALOFT SUGGESTS AN HEIGHTENED SEVERE WIND POTENTIAL.

ADDITIONAL SEVERE POTENTIAL APPEARS TO EXIST INVOF THE CENTRAL CONUS
DAY 6...THOUGH MODEL DIFFERENCES ARE SUFFICIENT TO COMPLICATE THE
FORECAST...AND THUS PRECLUDE AN AREAL HIGHLIGHT AT THIS POINT.

..GOSS.. 05/26/2009

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