DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 091249
SWODY1
SPC AC 091247

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0647 AM CST SUN DEC 09 2012

VALID 091300Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM E-CNTRL TX NEWD ACROSS THE
ARKLATEX TO THE MS VALLEY...

...SYNOPSIS...
A SHORTWAVE UPPER TROUGH EMBEDDED WITHIN BROAD LARGE-SCALE CYCLONIC
FLOW WILL DEEPEN ACROSS THE SRN ROCKIES AND EVENTUALLY REACH THE SRN
PLAINS BY MON MORNING. AS THIS OCCURS...A BELT OF STRONG DEEP-LAYER
SWLY FLOW WILL SHIFT SWD AND EXTEND FROM TX NEWD INTO THE GREAT
LAKES/NORTHEAST LATER TODAY. AN ASSOCIATED SFC COLD FRONT WILL
QUICKLY MOVE SWD...CONSOLIDATING WITH A WEAK WARM FRONT POSITIONED
FROM SRN OK EWD ACROSS THE TN VALLEY. A SEPARATE UPPER IMPULSE WILL
MOVE FROM NRN MX INTO CNTRL TX THIS AFTERNOON...BEFORE EVENTUALLY
PHASING WITH THE LARGE-SCALE CONUS TROUGH.

...E-CNTRL TX NEWD ACROSS THE ARKLATEX TO THE MS VALLEY...
EARLY MORNING RADAR DATA SHOW ELEVATED THUNDERSTORMS ONGOING IN A
WSW-ENE ORIENTED LOW-LEVEL WAA REGIME STRETCHING FROM CNTRL AR INTO
WRN KY...OCCURRING N OF A WARM FRONT EXTENDING FROM SRN AR EWD
ACROSS CNTRL AR AND NEWD ACROSS NWRN TN. THE ERN EXTENSION OF THE
WARM FRONT IS FORECAST TO SHIFT N OF THE OH VALLEY AS A WEAK SFC LOW
DEVELOPS...WITH ADDITIONAL TSTM DEVELOPMENT FOCUSED ACROSS THIS AREA
INTO A PROGRESSIVELY LESS UNSTABLE AIR MASS. MEANWHILE...A STRONG
COLD FRONT WILL MOVE ACROSS THE SRN PLAINS AND MID-MS RIVER VALLEY
TODAY...BECOMING POSITIONED FROM CNTRL TX AND ACROSS THE ARKLATEX
AND MID-MS RIVER VALLEY THIS AFTERNOON.

THE COLD FRONT WILL SERVE AS THE FOCUS FOR TSTM DEVELOPMENT THIS
AFTERNOON. MOISTURE RETURN IS ALREADY WELL UNDERWAY IN THE
PRE-FRONTAL AIR MASS /CHARACTERIZED BY MID-60S F DEWPOINTS/...AND
WILL YIELD MLCAPE VALUES RANGING FROM 500 J/KG ACROSS THE MID-MS
RIVER VALLEY TO 1500 J/KG ACROSS PARTS OF E TX WITH DAYTIME
HEATING....DESPITE MODEST MIDLEVEL LAPSE RATES IN PLACE.
STRENGTHENING DEEP-LAYER SWLY WIND FIELDS...WITH SLIGHT VEERING IN
THE LOWEST 3 KM AGL...WILL BE SUPPORTIVE OF SUPERCELL AND SMALL
CLUSTER DEVELOPMENT THIS AFTERNOON AS STRONGER FORCING FOR ASCENT
ASSOCIATED WITH THE UPPER TROUGH IS DISPLACED TO THE W. AN ENHANCED
RISK FOR A TORNADO OR TWO WILL EXIST ACROSS PARTS OF CNTRL/ERN AR
AND NRN LA...WHERE THE STRONGEST LOW-LEVEL WIND FIELDS WILL EXIST.
ADDITIONAL ISOLATED TSTMS COULD ALSO DEVELOP WITHIN THE WARM-SECTOR
ACROSS LA/E TX THIS AFTERNOON AND MAY POSE A SVR RISK...BUT WILL
REMAIN LESS FOCUSED WITHIN A WEAK LOW-LEVEL WAA REGIME.

MORE WIDESPREAD TSTM DEVELOPMENT IS FORECAST TO OCCUR ALONG THE
FRONT AFTER 10/00Z WITH A TRANSITION TO A LINEAR MODE EXPECTED TO
OCCUR...AS STRONGER MID-LEVEL HEIGHT FALLS OVERSPREAD THE REGION AND
LOW-LEVEL CONVERGENCE INCREASES ALONG THE COLD FRONT. 09/06Z NAM
FORECAST SOUNDINGS SUGGEST SUFFICIENT BOUNDARY LAYER MOISTURE WILL
BE IN PLACE FOR SFC-BASED CONVECTION OVERNIGHT...SUPPORTIVE OF AN
ISOLATED WIND AND TORNADO THREAT WITH SEWD PROGRESSION ACROSS THE
UPPER TX GULF COAST...NRN/WRN LA AND NRN MS. HOWEVER...DIURNAL
COOLING AND WEAKENING INSTABILITY SHOULD LEAD TO REDUCED SVR
POTENTIAL WITH TIME.

..ROGERS/THOMPSON.. 12/09/2012

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