DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 271650
SWODY2
SPC AC 271648

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1148 AM CDT SAT APR 27 2013

VALID 281200Z - 291200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
AN UPPER LEVEL SHORTWAVE TROUGH IS FORECAST TO SHIFT EWD ACROSS THE
OH VALLEY ON SUNDAY. AS THIS OCCURS...IT WILL BECOME DISLOCATED FROM
A POSITIVE TILT VORTICITY STREAMER EXTENDING SWWD INTO CNTRL TX AND
NRN MEXICO. AT THE SURFACE...LOW PRESSURE WILL BE POSITIONED OVER
THE LOWER/MID OH VALLEY AT THE START OF THE FORECAST PERIOD...WITH A
COLD FRONT TRAILING TO THE SW INTO CNTRL LA AND THEN WWD INTO CNTRL
TX. AS THE DAY PROGRESSES...THE LOW WILL WEAKEN AS IT LIFTS NEWD
INTO OH...AND THE TRAILING COLD FRONT WILL DISSIPATE BY LATE
AFTERNOON. MEANWHILE OVER THE NRN CONUS...A COLD FRONT ASSOCIATED
WITH A SURFACE CYCLONE OVER CANADA WILL MOVE SWD ACROSS THE
NRN/CNTRL PLAINS...AND WILL SERVE AS A FOCUS FOR THUNDERSTORM
DEVELOPMENT DURING THE AFTERNOON AND NIGHT.

...SRN HIGH PLAINS...
SELY LOW-LEVEL WINDS OVER MUCH OF TX WILL ENCOUNTER SWLY FLOW OVER
THE SRN HIGH PLAINS SUNDAY AFTERNOON...AND WILL RESULT IN A WEAK
ZONE OF SURFACE CONFLUENCE ORIENTED SWWD FROM WRN OK INTO W-CNTRL
TX. DEWPOINTS IN THE 30S TO LOW 40S COMBINED WITH TEMPERATURES IN
THE LOW 80S AND STEEP LOW TO MIDLEVEL LAPSE RATES WILL CONTRIBUTE
TOWARD MLCAPE VALUES FROM 500-1500 J/KG ALONG AND E OF THE
CONFLUENCE ZONE. THE UNSTABLE ENVIRONMENT COMBINED WITH A MINOR
DISTURBANCE MOVING SWD INTO THE AREA DURING THE AFTERNOON MAY BE
SUFFICIENT FOR ISOLATED TO SCATTERED THUNDERSTORM DEVELOPMENT.
THOUGH VERTICAL WIND PROFILES WILL BE UNFAVORABLE FOR ORGANIZED
THUNDERSTORM DEVELOPMENT...ISOLATED DAMAGING WIND GUSTS AND
MARGINALLY SEVERE HAIL CANNOT BE RULED OUT.

...CNTRL/ERN KY...SRN OH...
AS AN UPPER LEVEL SHORTWAVE TROUGH MOVES ENEWD ACROSS THE OH VALLEY
DURING THE AFTERNOON...A MIDLEVEL DRYSLOT IS FORECAST TO SPREAD
ACROSS CNTRL/ERN KY AND SRN OH. ANY CLEARING THAT TAKES PLACE WOULD
AID IN DESTABILIZING THE BOUNDARY LAYER...AND WITH 50S DEWPOINTS
PRESENT ACROSS THE AREA...COULD POTENTIALLY BOOST MLCAPE VALUES TO
500-1000 J/KG. ASCENT ASSOCIATED WITH THE UPPER DISTURBANCE COMBINED
WITH WEAKENING SURFACE CONVERGENCE TRAILING A LOW OVER ERN IND/WRN
OH MAY RESULT IN THE DEVELOPMENT OF A BROKEN LINE OF STORMS. LOW TO
MIDLEVEL SWLY FLOW ON THE ORDER OF 20-40 KT WILL BE MARGINALLY
FAVORABLE FOR ORGANIZED THUNDERSTORM DEVELOPMENT POSING A LOW-END
THREAT FOR SEVERE WIND/HAIL.

...SERN STATES...
THUNDERSTORMS ARE FORECAST TO BE ONGOING AT THE START OF THE PERIOD
FROM MIDDLE TN SWD INTO PORTIONS OF MS/AL. MORNING FORECAST
SOUNDINGS ACROSS THESE AREAS INDICATE SUFFICIENT CAPE AND VERTICAL
WIND SHEAR WILL BE PRESENT FOR AN ISOLATED DAMAGING WIND THREAT.
THEREAFTER...LAPSE RATES ARE EXPECTED TO WEAKEN SIGNIFICANTLY IN THE
LOW AND MIDLEVELS. THOUGH SHOWERS AND THUNDERSTORMS WILL LIKELY
CONTINUE THROUGH THE AFTERNOON...THE SEVERE WEATHER THREAT IS
FORECAST TO BECOME INCREASINGLY MARGINAL.

...SRN TX...
UNCERTAINTY EXISTS IN HOW MUCH RESIDUAL CLOUD COVER PRODUCED BY
OVERNIGHT CONVECTION WILL EXIST OVER SRN TX ON SUNDAY. IF HEATING
CAN OCCUR AND TEMPERATURES WARM INTO THE 80S...THEN LOW TO MID 60S
DEWPOINTS WILL AID IN MLCAPE VALUES NEAR 1000 J/KG. ESELY WINDS
OCCURRING OVER THE LOWEST 1 KM SURMOUNTED BY 30-40 KT WLY FLOW AT 6
KM WILL RESULT IN LONG HODOGRAPHS FAVORABLE FOR SPLITTING STORMS.
LATEST MODEL GUIDANCE INDICATES THUNDERSTORMS MAY MOVE EWD OUT OF
MEXICO AND INTO SRN TX DURING THE AFTERNOON AND EVENING. IF THIS
SCENARIO OCCURS...THEN ISOLATED LARGE HAIL WOULD BE POSSIBLE.

..GARNER.. 04/27/2013

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