SWODY1
SPC AC 212002
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0202 PM CST MON NOV 21 2011
VALID 212000Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE SRN
PLAINS INTO THE LOWER MS VALLEY...
...SRN PLAINS THROUGH LOWER MS VALLEY AREA...
QUASISTATIONARY FRONT EXTENDS FROM SRN AR SWWD THROUGH S-CNTRL AND
SWRN TX. THE FRONT WILL LIFT SLOWLY NWD THIS EVENING AND OVERNIGHT
AS LLJ STRENGTHENS IN RESPONSE TO EJECTING SHORTWAVE TROUGH. PRIMARY
THREAT THIS AFTERNOON INTO THE EARLY EVENING APPEARS TO BE ISOLATED
LARGE HAIL WITH ELEVATED STORMS DEVELOPING WITHIN ZONE OF ISENTROPIC
ASCENT NORTH OF THE BOUNDARY...ESPECIALLY FROM PARTS OF WRN THROUGH
N-CNTRL TX WHERE STEEPER MID-LEVEL LAPSE RATES RESIDE.
LATER THIS EVENING A PACIFIC FRONT WILL ACCOMPANY THE SHORTWAVE
TROUGH THROUGH WRN AND CNTRL TX. MODELS REMAIN CONSISTENT DEVELOPING
STORMS ALONG THIS CONVERGENCE ZONE ESPECIALLY FROM CNTRL THROUGH
N-CNTRL TX WHERE THE INFLUENCE OF DEEPER ASCENT WILL BE GREATER AND
THE ATMOSPHERE WILL BE LESS CAPPED. ACTIVITY WILL EVENTUALLY SHIFT
EWD INTO THE LOWER MS VALLEY REGION OVERNIGHT. PRIMARY THREAT WILL
BE ISOLATED DAMAGING WIND...BUT ISOLATED TORNADOES CANNOT BE RULED
OUT...ESPECIALLY FROM NERN TX INTO SWRN AR WHERE LARGE HODOGRAPHS
WILL EXIST ALONG STRENGTHENING LLJ.
..DIAL.. 11/21/2011
.PREV DISCUSSION... /ISSUED 1021 AM CST MON NOV 21 2011/
...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.
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