SWODY1
SPC AC 210545
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1145 PM CST SUN NOV 20 2011
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS TX/SRN OK EWD INTO CENTRAL
AR...
...SYNOPSIS...
A SHORTWAVE TROUGH...CURRENTLY LOCATED IN THE CA/NV REGION...IS
FORECAST TO SHIFT RAPIDLY EWD INTO NM TODAY...AND THEN ENEWD INTO
ERN KS OVERNIGHT. THIS UPPER SYSTEM WILL BECOME NEGATIVELY TILTED
DURING THE SECOND HALF OF THE PERIOD AS A 70-80 KT MID LEVEL JET MAX
MOVES FROM THE BASE ONTO THE EAST SIDE OF THE TROUGH.
...TX/SRN OK EWD INTO CENTRAL AR...
THE SEVERE FORECAST THIS FORECAST WILL BE COMPLICATED BY THE
PRESENCE OF AN EXISTING COLD SHALLOW AIR MASS...WITH THE LEADING
EDGE CURRENTLY EXTENDING FROM NERN AR SWWD INTO CENTRAL TX. MODELS
ARE CONSISTENT IN MAINTAINING SURFACE RIDGE ACROSS MUCH OF OK SWD
INTO CENTRAL TX TODAY AND GIVEN CONTINUED SLOW SWD MOTION OF FRONT
AND WEAK PRESSURE RISES...EXPECT FRONT IN CENTRAL TX TO REMAIN
QUASI-STATIONARY THROUGH MUCH OF THE DAY. HOWEVER...THE PORTION OF
THE FRONT IN AR/ERN TX MAY RETREAT SLOWLY WWD... POSSIBLY TO NEAR AN
AUS -HRO LINE BY EVENING...AS THE UPPER TROUGH APPROACHES.
GIVEN THE ABOVE FRONTAL LOCATION...THE GREATER HEIGHT
FALLS/DYNAMICAL FORCING WILL OCCUR NORTH AND WEST OF THE FRONT
THROUGH THE DAY. THE FORCING IS EXPECTED TO RESULT IN ELEVATED
STORMS FORMING EARLY IN THE DAY IN WRN TX...SPREADING RAPIDLY ENEWD
ACROSS NRN TX AND OK. DESPITE THE COLD BOUNDARY LAYER... MUCAPES
AROUND 1000 J/KG AND 50 KT DEEP LAYER SHEAR ABOVE THE BOUNDARY LAYER
WILL BE SUFFICIENT FOR SOME ROTATING STORMS...WITH HAIL THE PRIMARY
THREAT. AS THE STORMS PROGRESS AND APPROACH THE WARMER AND MORE
UNSTABLE BOUNDARY LAYER...THE POTENTIAL FOR WIND DAMAGE WILL
INCREASE FROM FAR ERN OK SWD INTO ERN TX. AS THE UPPER WAVE BECOMES
NEGATIVELY TILTED...A SURFACE WAVE SHOULD DEVELOP ALONG THE FRONT IN
AR MONDAY EVENING...AND THEN SHIFT NEWD INTO MO OVERNIGHT. ONCE THIS
HAPPENS...THE FRONT WILL BEGIN MOVING EWD WITH THE POTENTIAL FOR
MORE LINEAR STORMS TO DEVELOP ALONG IT. INSTABILITY IS NOT FORECAST
TO BE PARTICULARLY STRONG...THOUGH THE STRENGTH OF THE WIND FIELDS
AND SHEAR WILL BE FAVORABLE FOR WIND DAMAGE AND PERHAPS EVEN A
TORNADO OR TWO ...ESPECIALLY IN AR NEAR DEVELOPING SURFACE LOW.
ALSO...DURING THE AFTERNOON...THE UPPER FORCING MAY BRUSH THE
STATIONARY FRONT IN CENTRAL TX. THE FORECAST SOUNDINGS SHOW A WEAK
CAPPING INVERSION AROUND 700 MB...BUT IF SURFACE BASED STORMS CAN
DEVELOP NEAR THIS PORTION OF THE FRONT...MLCAPES NEAR 1500
J/KG...DEEP LAYER SHEAR AT 60 KT AND 1 KM SRH AOA 200 M2/S2 WILL BE
FAVORABLE FOR SUPERCELLS...INCLUDING TORNADOES. THE SEVERE THREAT
WILL DECREASE DURING THE EVENING AS THE FORCING LIFTS NWD OUT OF THE
REGION.
..IMY/LEITMAN.. 11/21/2011
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