Monday, November 21, 2011

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211623
SWODY1
SPC AC 211621

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1021 AM CST MON NOV 21 2011

VALID 211630Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF TX/OK/AR/LA...

...NORTH TX/SOUTHERN OK...
A PAIR OF POWERFUL UPPER SYSTEMS IS MOVING THROUGH THE SOUTHWEST
UNITED STATES...AND WILL AFFECT PARTS OF TX AND THE LOWER MS VALLEY
DURING THIS FORECAST PERIOD. THE PRIMARY SYSTEM FOR FOCUSING THE
SEVERE THREAT IS A SUB-TROPICAL SHORTWAVE TROUGH MOVING ACROSS
NORTHERN MEXICO AND INTO SOUTHWEST TX. LIFT AHEAD OF THIS TROUGH
HAS RESULTED IN THE DEVELOPMENT OF A CLUSTER OF ELEVATED
THUNDERSTORMS OVER WEST TX NEAR LBB. INCREASING FORCING FOR ASCENT
AND TRANSPORT OF ELEVATED MOIST/UNSTABLE AIR NORTHWARD INTO REGION
WILL PROMOTE CONTINUED EXPANSION AND INTENSIFICATION OF THESE STORMS
THROUGH THE AFTERNOON. SUFFICIENT CAPE ALOFT AND STEEP LAPSE
RATES...COUPLED WITH STRONG DEEP LAYER SHEAR...SUGGEST A RISK OF A
FEW INTENSE UPDRAFTS CAPABLE OF LARGE HAIL. THIS THREAT WILL SPREAD
EASTWARD THROUGH THE DAY ACROSS SOUTHERN OK AND NORTH TX.

...CENTRAL TX...
THERE IS CONSIDERABLE UNCERTAINTY WHETHER MUCH CONVECTION WILL FORM
IMMEDIATELY ALONG THE FRONT STALLED ACROSS CENTRAL TX. FORCING THAT
FAR SOUTH IS RELATIVELY WEAK. ALSO...MID LEVEL TEMPERATURES ARE
RATHER WARM AT THAT LATITUDE SUGGESTING CONVECTIVE INITIATION WILL
BE HARDER TO ATTAIN. ANY STORM THAT CAN BECOME ESTABLISHED ALONG
THE BOUNDARY WOULD POSE A RISK OF GUSTY WINDS OR EVEN A BRIEF
TORNADO.

...EASTERN OK/AR...
LATER THIS AFTERNOON AND EVENING...LARGE SCALE FORCING WILL BEGIN TO
SPREAD FARTHER EAST INTO EASTERN OK AND AR. SURFACE-BASED
INSTABILITY MAY REMAIN IN THIS AREA...INCREASING THE RISK FOR
GUSTY/DAMAGING WINDS AS WELL AS LARGE HAIL IN THE STRONGEST STORMS.

..HART/COHEN.. 11/21/2011

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