MESO: Mesoscale Discussion 2123

ACUS11 KWNS 262134
SWOMCD
SPC MCD 262134
LAZ000-ARZ000-TXZ000-262300-

MESOSCALE DISCUSSION 2123
NWS STORM PREDICTION CENTER NORMAN OK
0334 PM CST MON NOV 26 2012

AREAS AFFECTED...NERN TX...NRN LA...EXTREME SRN AR

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 262134Z - 262300Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS NERN TX...NRN
LA AND EXTREME SRN AR LATE THIS AFTERNOON AND EVENING. ACTIVITY WILL
EVENTUALLY EVOLVE INTO A LINE AS A COLD FRONT ADVANCES EWD ACROSS
THE AREA. STORMS WILL PRIMARILY POSE A DAMAGING WIND AND LARGE HAIL
THREAT. A WW MAY NEED TO BE ISSUED DURING THE NEXT COUPLE OF HOURS.

DISCUSSION...MESOANALYSIS AT 21Z PLACES A SURFACE LOW IN FAR NERN
TX...WITH A WARM FRONT SLOWLY RETREATING EWD INTO CNTRL PORTIONS OF
LA...AND A COLD FRONT ADVANCING E-SEWD ACROSS CNTRL TX. AMPLE
SUNSHINE HAS AIDED IN WARM SECTOR TEMPERATURES WARMING INTO THE 70S
TO LOW 80S...WHILE AN AXIS OF LOW TO MID 60S DEWPOINTS EXTENDS
N-NEWD FROM THE TX GULF COAST INTO WRN LA. THE WARM/MOIST BOUNDARY
LAYER COMBINED WITH 700-500 MB LAPSE RATES NEAR 7 C/KM IS YIELDING
MLCAPE VALUES ESTIMATED TO BE AROUND 1000-2000 J/KG AHEAD OF THE
COLD FRONT.

VISIBLE SATELLITE IMAGERY AS OF 2115Z SHOWS THE WARM SECTOR IS
CAPPED...WHICH IS ALSO SUPPORTED BY 18Z SHV RAOB.
HOWEVER...LARGE-SCALE ASCENT ASSOCIATED WITH A SERIES OF SRN STREAM
DISTURBANCES EMANATING OUT OF NRN MEXICO...COMBINED WITH FRONTAL
CONVERGENCE/ASCENT ARE FORECAST TO ERODE THE CAPPING INVERSION
DURING THE 22-00Z TIME PERIOD. THIS WILL FAVOR THUNDERSTORM
DEVELOPMENT ALONG THE COLD FRONT AND PERHAPS EWD INVOF THE SURFACE
LOW AND WARM FRONT. DEEP-LAYER SHEAR ON THE ORDER OF 30-40 KT WILL
SUPPORT MULTICELL CLUSTERS AND PERHAPS A FEW SUPERCELLS POSING A
THREAT FOR LARGE HAIL AND DAMAGING WIND GUSTS. LOW-LEVEL SHEAR
PROFILES WILL NOT BE PARTICULARLY STRONG...THUS ANY TORNADO THREAT
IS EXPECTED TO BE BRIEF AND FOCUSED NEAR THE LOW WHERE BACKED
SURFACE WINDS WILL BE MOST PROBABLE.

BY NIGHT...STORMS ARE FORECAST TO ORGANIZE INTO A LINE AS THE COLD
FRONT ADVANCES EWD...WITH THE THREAT FOR HAIL AND STRONG/SVR WIND
GUSTS CONTINUING.

..GARNER/EDWARDS.. 11/26/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...JAN...LCH...SHV...HGX...FWD...

LAT...LON 30849533 31499614 32559605 33229461 33279249 32889138
31999124 31479198 30929358 30849533

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