MESO: Mesoscale Discussion 2160

ACUS11 KWNS 161100
SWOMCD
SPC MCD 161100
MSZ000-LAZ000-ARZ000-TXZ000-161230-

MESOSCALE DISCUSSION 2160
NWS STORM PREDICTION CENTER NORMAN OK
0500 AM CST SUN DEC 16 2012

AREAS AFFECTED...PORTIONS OF THE MIDDLE AND UPPER TX COASTAL PLAIN
INTO CENTRAL/NRN LA AND EXTREME SWRN-WEST CENTRAL MS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 161100Z - 161230Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...A SVR TSTM WATCH MAY BE NEEDED ACROSS THE MIDDLE AND UPPER
TX COASTAL PLAIN TO SWRN-WEST CENTRAL MS BY 12Z.

TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY THIS
MORNING /BY 12Z/ ACROSS THE WRN AND CENTRAL PORTION OF THE
DISCUSSION AREA...WITH STORMS ADVANCING ENEWD INTO LA AND EVENTUALLY
REACHING SWRN-WEST CENTRAL MS BETWEEN 16-18Z. SHEAR VECTORS
ORIENTED NEARLY PARALLEL TO A SURFACE BOUNDARY SUGGEST LEWPS AND
LINE SEGMENTS WILL BE THE PRIMARY STORM MODES WITH SOME SUPERCELLS
POSSIBLE GIVEN THE STRENGTH OF THE SHEAR. THUS...DAMAGING WINDS
SHOULD BE THE PRIMARY THREAT...THOUGH A TORNADO CANNOT BE RULED OUT.

DISCUSSION...DESPITE WEAK LAPSE RATES...MILD/ABOVE NORMAL SURFACE
TEMPERATURES /UPPER 60S-LOWER 70S/ FOR MID DECEMBER ACROSS THE
DISCUSSION AREA FOR THIS TIME OF DAY COMBINED WITH DEWPOINTS IN THE
MID 60S TO AROUND 70 F ARE AIDING IN A MODERATELY UNSTABLE AIR MASS.
AT 10Z...OBJECTIVE ANALYSIS INDICATED MUCAPE RANGING FROM 1000 J/KG
IN SWRN LA TO 1500-2000 J/KG IN THE MID-UPPER TX COASTAL PLAIN.
TRENDS IN REGIONAL RADAR IMAGERY /SINCE 09Z/ SHOWED AN INCREASE IN
THE COVERAGE OF SHALLOW CONVECTION OVER SOUTHEAST TX INTO CENTRAL/
NRN LA. MEANWHILE...TSTMS HAD DEVELOPED SINCE 10Z FARTHER INLAND TO
THE W/NW OF A SURFACE BOUNDARY WHICH EXTENDED FROM DEEP S TX /INVOF
HEBBRONVILLE/ NNEWD TO BASTROP COUNTY AND THEN NEWD TO THE NW OF
LFK.

CONVECTION ALLOWING MODELS ARE IN AGREEMENT THAT THIS RECENT
INCREASE SHALLOW CONVECTION AND THE MORE RECENT TSTM DEVELOPMENT ARE
LIKELY THE BEGINNING STAGES OF A MORE SUBSTANTIAL UPTICK IN TSTM
COVERAGE/INTENSITY EXPECTED BY 12Z OVER THE TX PORTION OF THE
DISCUSSION AREA. THIS ACTIVITY IS IN RESPONSE TO INCREASING UPWARD
VERTICAL MOTION SPREADING ENEWD IN ADVANCE OF A PROGRESSIVE THOUGH
SOMEWHAT WEAK UPSTREAM SHORTWAVE TROUGH...NOW LOCATED OVER SW TX.
THIS FEATURE IS EXPECTED TO REACH CENTRAL TO EAST TX BY 18Z...WITH
WEAK HEIGHT FALLS SUGGESTING A FURTHER INCREASE IN TSTMS WILL BE
LIKELY. STORMS SHOULD REACH SWRN-WEST CENTRAL MS BETWEEN
16-18Z...SUGGESTING THIS REGION MAY BE INCLUDED IN A WATCH. STRONG
SWLY FLOW ALOFT IS MORE THAN SUFFICIENT TO SUPPORT ORGANIZED
STORMS...WITH DAMAGING WINDS BEING THE PRIMARY THREAT. SMALL
HODOGRAPH CURVATURE SUGGESTS A LESSER THREAT FOR A TORNADO...THOUGH
THIS THREAT CANNOT BE RULED OUT.

..PETERS/EDWARDS.. 12/16/2012

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

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

LAT...LON 29429697 30659734 31449608 32039463 32839295 33079078
32279047 31109082 30269325 29149584 29059651 29429697

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