MESO: Mesoscale Discussion 2207

ACUS11 KWNS 251446
SWOMCD
SPC MCD 251446
MSZ000-LAZ000-TXZ000-251545-

MESOSCALE DISCUSSION 2207
NWS STORM PREDICTION CENTER NORMAN OK
0846 AM CST TUE DEC 25 2012

AREAS AFFECTED...E AND SE TX/WRN AND NRN LA/PART OF WEST
CENTRAL-SWRN MS

CONCERNING...SEVERE THUNDERSTORM WATCH 691...

VALID 251446Z - 251545Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 691
CONTINUES.

SUMMARY...A NEW SVR TSTM WATCH WILL BE COORDINATED BY 1450Z WITH
AFFECTED WFO/S FROM NE/E TX THROUGH NRN LA TO WEST CENTRAL-SWRN
MS...WITH HAIL AND A LOCAL STRONG WIND GUST POSSIBLE.

A TORNADO WATCH IS LIKELY TO BE ISSUED FOR MUCH OF SERN TX/UPPER TX
COAST AREA INTO SWRN LA TO THE WEST OF WW 692...AS AN INCREASE IN
SURFACE-BASED DEVELOPMENT IS EXPECTED AFTER 15Z.

DISCUSSION...EARLY MORNING TRENDS IN UPPER AIR DATA/SATELLITE
IMAGERY SHOWED A VIGOROUS...DIGGING SHORTWAVE TROUGH MOVING ESEWD
ACROSS WRN INTO CENTRAL TX...WITH 140 METER/12 HR 500 MB HEIGHT
FALLS AT 12Z AT MAF. STRONG FORCING FOR ASCENT/DPVA WILL SPREAD EWD
INTO E TX/LOWER MS VALLEY TODAY. AT 14Z...A WARM FRONT EXTENDED EWD
FROM A SURFACE LOW NEAR CLL THROUGH SRN LA /60-80 MILES N OF THE
GULF COAST/ AND INTO FAR SERN MS TO ALONG THE COAST OF THE WRN FL
PANHANDLE.

...NERN TX/NRN LA/WEST CENTRAL-SWRN MS...
REGIONAL RADAR IMAGERY SHOWED ONGOING TSTMS ALONG AND N OF THE WARM
FRONT IN MUCH OF THE NERN QUARTER OF TX...WITH THIS ACTIVITY
EXPECTED TO DEVELOP/ADVANCE ENEWD INTO NRN LA AND EVENTUALLY WEST
CENTRAL-SWRN MS THIS MORNING AND AFTERNOON. STEEP MIDLEVEL LAPSE
RATES AOA 8 C/KM PER 12Z TX AND LCH SOUNDINGS AND STRONG EFFECTIVE
BULK SHEAR EXCEEDING 60 KT WILL SUPPORT ELEVATED SUPERCELLS WITH
HAIL BEING THE PRIMARY THREAT. HOWEVER...A LOCALLY STRONG WIND GUST
CANNOT BE RULED OUT...ESPECIALLY WHERE THE BOUNDARY LAYER IS MORE
SHALLOW.

...SERN TX TO SWRN LA...
STRONG VERTICALLY VEERING WINDS ARE RESULTING IN EFFECTIVE SRH OF
300-400 MS/S2 ALONG AND S OF THE WARM FRONT. THESE VALUES ARE
EXPECTED TO INCREASE THIS MORNING/EARLY AFTERNOON AS THE LLJ
STRENGTHENS TO AROUND 50 KT AND A 90-100 KT WLY MIDLEVEL JET
TRANSLATES EWD INTO SE TX...LA AND SRN MS. THIS COMBINED WITH
MODERATE INSTABILITY AND STRONG BULK SHEAR WILL SUPPORT WELL
ORGANIZED STORMS/SUPERCELLS. WATER VAPOR IMAGERY INDICATED SOME
POTENTIAL SUBSIDENCE IN THE WAKE OF A LEAD IMPULSE IN THE NWRN GULF.
HOWEVER...STRONG/DEEP LAYER ASCENT WILL MOVE INTO SERN TX THIS
MORNING...PROMOTING SURFACE-BASED TSTM DEVELOPMENT AND THE THREAT
FOR TORNADOES.

..PETERS/EDWARDS.. 12/25/2012

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

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

LAT...LON 31459601 32399515 32699297 32619093 32199065 31359145
31039175 30559251 29629263 29619335 29199464 28599583
28299625 29759624 31459601

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