DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 271256
SWODY1
SPC AC 271254

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0754 AM CDT SAT APR 27 2013

VALID 271300Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FROM SW TX TO NW MS/SW TN...

...SYNOPSIS...
A WEAK MIDLEVEL LOW OVER SE KS...AND A TRAILING SHORTWAVE TROUGH
OVER CENTRAL/ERN OK...WILL MOVE EWD TO THE TN AND LOWER OH VALLEY
REGIONS BY EARLY SUNDAY. AT THE SURFACE...A WEAK LOW IN SE OK WILL
TRANSLATE NEWD TO THE LOWER OH VALLEY ALONG A PRE-EXISTING
BAROCLINIC ZONE...IN ADVANCE OF THE MIDLEVEL TROUGH. A SWATH OF
MID-UPPER 60S BOUNDARY LAYER DEWPOINTS HAS SPREAD INLAND ACROSS LA
AND SRN/ERN TX. THIS MOIST SECTOR WILL EXPAND TODAY ACROSS SE
AR/NRN MS/NW AL AND WRN/MIDDLE TN...IMMEDIATELY S OF THE FRONT THAT
WILL BE REINFORCED BY CONVECTION THIS MORNING.

...SE AR/NW MS/SW TN THIS AFTERNOON INTO EARLY TONIGHT...
MLCAPE VALUES ARE EXPECTED TO REACH THE 1500-2500 J/KG RANGE BY
AFTERNOON WITH SURFACE HEATING ON THE SRN FRINGE OF THE MORNING
CLOUDS/CONVECTION...AS LOW-LEVEL MOISTURE INCREASES FROM THE S/SW.
MEANWHILE...DEEP-LAYER VERTICAL SHEAR WILL BE FAVORABLE FOR
ORGANIZED CLUSTERS/LINE SEGMENTS...AS WELL AS SUPERCELLS...AS THE
SHORTWAVE TROUGH PIVOTS EWD FROM OK TO AR. THE PRIMARY SEVERE RISKS
WILL BE DAMAGING GUSTS AND LARGE HAIL WITH A BAND OF STORMS NEAR THE
SURFACE LOW AND ALONG THE TRAILING COLD FRONT THIS AFTERNOON THROUGH
EARLY TONIGHT. THOUGH LOW-LEVEL SHEAR WILL NOT BE PARTICULARLY
STRONG...SOME ENHANCEMENT TO HODOGRAPH CURVATURE AND RESULTANT
EFFECTIVE SRH NEAR 200 M2/S2 COULD SUPPORT AN ISOLATED TORNADO THIS
AFTERNOON/EVENING FROM ERN AR INTO NW MS/SW TN.

...TX BIG BEND/RIO GRANDE VALLEY THIS AFTERNOON INTO TONIGHT...
BOUNDARY LAYER DEWPOINTS IN THE 68-70 F RANGE HAVE OVERSPREAD S AND
SE TX THIS MORNING...BENEATH A RESIDUAL STEEP MIDLEVEL LAPSE RATE
PLUME. THOUGH THE PRIMARY SYNOPTIC WAVE WILL PROGRESS AWAY FROM
THIS AREA THROUGH TONIGHT...A BAND OF 30-40 KT WSWLY MIDLEVEL FLOW
WILL PERSIST INVOF THE SLOW-MOVING FRONT ACROSS SW AND CENTRAL TX.
THUS...THE COMBINATION OF BUOYANCY AND VERTICAL SHEAR WILL BE
FAVORABLE FOR ORGANIZED CLUSTERS AND SUPERCELLS AS STORMS FORM LATE
THIS AFTERNOON ALONG THE FRONT FROM SW INTO CENTRAL TX...AS WELL AS
OVER THE HIGH TERRAIN IN NE MEXICO. LARGE HAIL WILL BE THE PRIMARY
RISK INITIALLY WITH SPLITTING STORMS. OUTFLOW MERGERS AND UPSCALE
GROWTH SHOULD SUPPORT SOME INCREASE IN THE DAMAGING WIND RISK THIS
EVENING INTO EARLY TONIGHT...AS STORMS PROPAGATE SEWD INTO S TX
BEFORE WEAKENING.

...E TX AREA THIS AFTERNOON...
THOUGH LARGE SCALE FORCING FOR ASCENT MAY REMAIN RATHER WEAK THROUGH
THIS AFTERNOON...SUBSTANTIAL SURFACE HEATING AND LOW-LEVEL
CONVERGENCE ALONG A SURFACE COLD FRONT MAY PROMOTE THUNDERSTORM
DEVELOPMENT. MLCAPE WILL POTENTIALLY REACH 2500 J/KG WITH STEEP
MIDLEVEL LAPSE RATES...THOUGH LOW-LEVEL FLOW/SHEAR WILL REMAIN WEAK.
THE NET RESULT WILL BE AN ENVIRONMENT SUPPORTIVE OF LARGE HAIL...AND
THERE WILL BE ENOUGH OF A RISK FOR THUNDERSTORM INITIATION TO
WARRANT EXPANSION OF THE CATEGORICAL SLIGHT RISK INTO THIS AREA FOR
THIS AFTERNOON.

..THOMPSON/COHEN.. 04/27/2013

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