DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 150901
SWOD48
SPC AC 150900

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT WED MAY 15 2013

VALID 181200Z - 231200Z

...DISCUSSION...
A SEVERAL DAY EPISODE OF FAIRLY SUBSTANTIAL SEVERE WEATHER APPEARS
LIKELY ACROSS THE CENTRAL U.S. BEGINNING DAY 4 /SAT. 5-18/...AND
LIKELY CONTINUING THROUGH AT LEAST DAY 6 /MON. 5-20/.

MEDIUM-RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH MUCH OF THE
PERIOD...AS AN UPPER TROUGH CROSSING THE ROCKIES AT THE START OF THE
PERIOD BEGINS AFFECTING THE PLAINS DAY 4. THE TROUGH IS THEN
PROGGED TO ENTER THE PLAINS DAY 5...AND THEN EVOLVE INTO A CLOSED
LOW DAY 6 AS A SECONDARY SPEED MAX ROTATES OUT OF THE ROCKIES AND
INTO THE PLAINS.

AS THE TROUGH EVOLVES...A STRENGTHENING SURFACE SYSTEM IS LIKEWISE
EXPECTED TO MOVE ACROSS THE CENTRAL CONUS...LIKELY FOCUSING DAILY
DEVELOPMENT OF WIDESPREAD STORMS. WHILE CAPPING WILL LIKELY BE AN
ISSUE -- LIMITING COVERAGE OF CONVECTION ALONG SRN REACHES OF THIS
DEVELOPING SYSTEM...EXPECT THAT STRONG LARGE-SCALE ASCENT WILL
PERMIT RELATIVELY WIDESPREAD CONVECTION OVER CENTRAL PORTIONS OF THE
COUNTRY FOR SEVERAL DAYS IN A ROW.

THE GREATEST THREAT DAY 4 WILL LIKELY RESIDE FROM THE DAKOTAS SWD
INTO NRN KS...AS VERY STEEP LAPSE RATES CONTRIBUTE TO STRONG
DESTABILIZATION AND THE ERN FRINGE OF STRONGER FLOW ALOFT BEGINS TO
OVERSPREAD THE REGION. LARGE HAIL AND DAMAGING WINDS WILL LIKELY BE
THE MAIN THREATS DAY 4.

DAY 5...STRONG DESTABILIZATION IS AGAIN FORECAST WHICH -- COMBINED
WITH FAVORABLE SHEAR SPREADING FARTHER E...SUGGESTS THAT THREAT FOR
LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES SHOULD EXTEND
FROM THE MID MO VALLEY REGION SWD INTO KS/MO/OK AND VICINITY.

ATTM...IT APPEARS THAT DAY 6 MAY BE THE DAY OF HIGHEST TORNADO
POTENTIAL...AS A REINFORCING MID-LEVEL SPEED MAX SHIFTS INTO THE
CENTRAL PART OF THE COUNTRY. THE MAIN AXIS OF SEVERE WEATHER
APPEARS LIKELY TO EXTEND FROM THE IA/IL AREA SWWD ACROSS MO INTO
PARTS OF KS/OK/AR DURING THE AFTERNOON AND EVENING HOURS.

THREAT MAY CONTINUE DAY 7...A BIT FARTHER E THAN DAY 6...BUT MORE
UNCERTAINTY AND HINTS OF SOMEWHAT DECREASED SEVERE POTENTIAL ARE
EVIDENT ATTM. THUS...NO OUTLOOK AREAS WILL BE ISSUED BEYOND DAY 6
ATTM.

..GOSS.. 05/15/2013

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