DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 090557
SWODY1
SPC AC 090554

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1154 PM CST SAT DEC 08 2012

VALID 091200Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM FAR SERN MO/FAR WRN KY/WRN
TN THROUGH THE ARKLATEX REGION TO E AND S CENTRAL TX...

...SYNOPSIS...
A LARGE SCALE TROUGH WILL CONTINUE TO ENCOMPASS MUCH OF INTERIOR
NORTH AMERICA THIS FORECAST PERIOD. MODELS SUGGEST THE PHASING OF
SEVERAL EMBEDDED SHORTWAVE TROUGHS TODAY SHOULD LEAD TO SHARPENING
OF A POSITIVELY-TILTED LARGE SCALE TROUGH EXTENDING FROM THE TX BIG
BEND TO NRN ONTARIO. AS THIS EVOLUTION OCCURS...DEEP LAYER SWLY WIND
FIELDS WILL BE STRENGTHENING FROM TX TO THE LOWER-MID MS VALLEY TO
THE NERN STATES. A SUB-TROPICAL SHORTWAVE TROUGH...CURRENTLY MOVING
ACROSS SRN BAJA PER WATER VAPOR IMAGERY...IS EXPECTED TO REACH THE
MID-UPPER TX COAST REGION LATE THIS AFTERNOON. THIS FEATURE SHOULD
SUPPORT A TSTM POTENTIAL ALONG THE SRN EXTENT OF A SURFACE FRONT
AND/OR IN THE WARM SECTOR INTO LA.

THE SHARPENING OF THE DEEP PARENT TROUGH WITH GREATEST SURFACE
PRESSURE FALLS EXPECTED ALONG AND E OF THE MID MS VALLEY SUGGESTS
THE PRIMARY SURFACE LOW WILL FORM NEAR TO EAST OF KSTL THIS
AFTERNOON. THIS FEATURE WILL THEN INTENSIFY SOME TONIGHT AS IT
TRACKS THROUGH THE OH VALLEY TO THE LOWER GREAT LAKES REGION BY 12Z
MON. ALTHOUGH A COLD FRONT WILL BE MOVING SEWD THROUGH THE CENTRAL
PLAINS TO NWRN TX AT THE START OF DAY 1...A SEPARATE BOUNDARY
EXTENDING FROM CENTRAL OK TO SRN/CENTRAL MO SHOULD BECOME THE
PRIMARY FRONT. THIS BOUNDARY WILL BE FOCUS FOR TSTM DEVELOPMENT AS
THIS FRONT ADVANCES E/SEWD INTO THE OH/TN AND LOWER MS VALLEYS.

...S CENTRAL-ERN TX/NRN LA/AR/WRN-NRN MS/WRN TN/WRN KY/SERN MO...
TSTMS...MAINLY ELEVATED...ARE EXPECTED TO BE ONGOING AT 12Z TODAY IN
VICINITY AND N OF THE PRIMARY SURFACE BOUNDARY FROM PARTS OF ERN OK
AND AR TO THE TN AND LOWER OH VALLEYS. ACTIVITY IN THE WRN EXTENT OF
THIS REGION COULD BE STRONG ENOUGH TO POSE A THREAT FOR ONGOING
ISOLATED HAIL INTO EARLY SUN MORNING.

MEANWHILE...SWLY LOW LEVEL WINDS AHEAD OF THE PRIMARY FRONT WILL
MAINTAIN NEWD MOISTURE RETURN WITH SURFACE DEWPOINTS AROUND 60
REACHING FAR WRN TN AND ADJACENT NERN AR/FAR SERN MO THIS
AFTERNOON...WITH MID-UPPER 50S POSSIBLE INTO CENTRAL KY/SWRN OH.
MID 60S F DEWPOINTS WILL BE INTO SRN AR WITH UPPER 60S CONFINED
ALONG AND INLAND OF THE TX COAST. GENERALLY WEAK MIDLEVEL LAPSE
RATES WILL BE THE PRIMARY LIMITING FACTOR FOR STRONGER INSTABILITY
TODAY...THOUGH MOISTURE RETURN AND SURFACE HEATING SHOULD RESULT IN
MLCAPE 500-1200 J/KG ACROSS THE SLIGHT RISK AREA. THE GREATER
INSTABILITY WILL BE CONFINED TO OVER AND S OF SRN AR...WHERE MLCAPE
WILL EXCEED 1000 J/KG.

THE MORNING TSTMS WILL SHIFT NEWD INTO THE OH VALLEY AS A SWLY LLJ
MOVES INTO THIS REGION SUPPORTING A CONCURRENT NEWD TRANSLATION OF
THE WAA REGIME. NEW TSTM DEVELOPMENT IS EXPECTED THIS AFTERNOON SWWD
ALONG THE FRONT AS IT BEGINS TO MOVE SEWD INTO AR...NERN TX AND
INLAND FROM THE MIDDLE TX COAST. EFFECTIVE BULK SHEAR OF 40-50 KT
WITHIN THE STRENGTHENING DEEP LAYER WIND FIELD WILL SUPPORT
ORGANIZATION WITH DAMAGING WINDS AND HAIL THE PRIMARY THREATS.
HOWEVER...ANY DISCRETE STORMS...GIVEN THE STRENGTH OF THE DEEP LAYER
SHEAR...COULD POSE A TORNADO THREAT. A GREATER TORNADO THREAT MAY
DEVELOP SUN EVENING OVER NRN LA INTO SERN AR AND WRN MS...AS A
SECONDARY SWLY LLJ STRENGTHENS IN RESPONSE TO HEIGHT FALLS AS
SHORTWAVE TROUGH APPROACHES THE SRN PLAINS FROM THE FOUR CORNERS.
THE SEVERE WEATHER THREAT SHOULD DIMINISH LATE SUN EVENING AS THE
BOUNDARY LAYER STABILIZES. TSTMS WILL...HOWEVER...PERSIST OVERNIGHT
ALONG THE FRONT AS STRONGER HEIGHT FALLS ADVANCE EWD WITH THE
FULL-LATITUDE PARENT TROUGH SUPPORTING LINEAR FORCING.

..PETERS/MOSIER.. 12/09/2012

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