SWODY1
SPC AC 211256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0656 AM CST MON NOV 21 2011
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON THROUGH TONIGHT
FOR CENTRAL/N TX ACROSS SRN/ERN OK INTO WRN/CENTRAL AR...
...TX/OK/AR AREA THROUGH TONIGHT...
A WELL-DEFINED SHORTWAVE TROUGH OVER NW BAJA AND THE LOWER CO RIVER
VALLEY WILL PROGRESS GENERALLY EWD TO W TX BY THIS EVENING...AND
CONTINUE NEWD ACROSS N TX/OK/KS OVERNIGHT. IN ADVANCE OF THE
MIDLEVEL TROUGH...A SHALLOW COLD AIR MASS HAS SPREAD SWD INTO
CENTRAL AR AND NE/CENTRAL TX. THE STRONGER FORCING FOR ASCENT TODAY
WILL OCCUR ABOVE THE SHALLOW STABLE LAYER ACROSS TX/OK...AND
NOTEWORTHY SURFACE CYCLOGENESIS IS NOT EXPECTED UNTIL TONIGHT AS THE
MIDLEVEL WAVE BEGINS TO PHASE MORE CLEARLY WITH THE SURFACE FRONT
ACROSS AR.
LOW-LEVEL SLY FLOW AND WAA WILL INCREASE ABOVE THE SHALLOW COLD AIR
MASS BY AFTERNOON ACROSS CENTRAL/N TX IN RESPONSE TO THE APPROACH OF
THE MIDLEVEL TROUGH. MEANWHILE...A MOIST BOUNDARY LAYER WITH
DEWPOINTS OF 68-72 F S OF THE FRONT WILL CONTRIBUTE TO SATURATION IN
THE DEVELOPING WAA REGIME...AND MIDLEVEL LAPSE RATES OF 6.5-7 C/KM
WILL SUPPORT MUCAPE OF 1500-2000 J/KG. THIS INSTABILITY...IN
COMBINATION WITH EFFECTIVE BULK SHEAR OF 40-50 KT...WILL BE
SUFFICIENT FOR A RISK OF ELEVATED SUPERCELLS CAPABLE OF PRODUCING
LARGE HAIL. THE HAIL RISK IS EXPECTED TO BEGIN AROUND MIDDAY-EARLY
AFTERNOON ACROSS NW TX...AND THEN SPREAD NEWD THROUGH THE
AFTERNOON/EVENING.
THE POTENTIAL FOR SURFACE-BASED STORMS ALONG AND S OF THE SURFACE
FRONT IS MORE UNCERTAIN THIS AFTERNOON. AT LEAST WEAK CONVECTIVE
INHIBITION SHOULD BE MAINTAINED IN THE WARM SECTOR S OF THE FRONT
THIS AFTERNOON...AND ASCENT WILL BE FOCUSED N OF THE SURFACE
BOUNDARY IN THE ANAFRONTAL FLOW REGIME. IF STORMS DO FORM AND MOVE
ALONG THE SURFACE FRONT...THE ENVIRONMENT WILL BE SUPPORTIVE OF SOME
TORNADO RISK...IN ADDITION TO LARGE HAIL AND ISOLATED DAMAGING
WINDS. OVERNIGHT...A BAND OF STORMS BASED NEAR THE SURFACE ALONG
FRONT WILL PERSIST NEAR THE PATH OF THE SURFACE LOW ACROSS NE TX
INTO AR...AND ALONG THE TRAILING COLD FRONT IN CENTRAL TX.
..THOMPSON/JIRAK.. 11/21/2011
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