DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 130832
SWODY3
SPC AC 130830

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CST THU DEC 13 2012

VALID 151200Z - 161200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
A STRONG SOUTHWESTERLY UPPER JET WILL PERSIST IN A BROAD
ANTICYCLONIC ARC ACROSS THE CENTRAL AND SOUTHERN TIER STATES EAST OF
THE ROCKIES DURING THIS PERIOD. SOME EASTWARD PROPAGATION APPEARS
LIKELY...THOUGH...AS A STRONG UPSTREAM MID-LATITUDE JET BEGINS TO
NOSE INLAND ACROSS THE NORTHERN PACIFIC COAST. MODELS INDICATE THAT
A SIGNIFICANT SHORT WAVE IMPULSE ASSOCIATED WITH THE LEAD FEATURE
WILL BEGIN TO WEAKEN AS IT MIGRATES NORTHEAST OF THE MISSOURI VALLEY
INTO THE GREAT LAKES REGION...ACCOMPANIED BY A SLOWLY FILLING /BUT
STILL AROUND 1000 MB/ SURFACE CYCLONE. AT THE SAME TIME...ANOTHER
SHORT WAVE IMPULSE MAY EMERGE FROM THE SOUTHWESTERN U.S...AND
CONTRIBUTE TO SECONDARY SURFACE CYCLOGENESIS ALONG THE TRAILING
SURFACE FRONT ACROSS THE SOUTH CENTRAL PLAINS.

MUCH VARIABILITY EXISTS AMONG THE MODELS CONCERNING THIS LATTER
FEATURE. HOWEVER...MOST GUIDANCE DOES INDICATE THAT THE PRE-FRONTAL
ENVIRONMENT WILL BE CHARACTERIZED BY AT LEAST MODERATELY STRONG AND
SHEARED MEAN WEST SOUTHWESTERLY LOWER/MID TROPOSPHERIC FLOW
/INCLUDING SIZABLE LOW-LEVEL HODOGRAPHS/...FROM THE LOWER
MISSISSIPPI VALLEY INTO THE APPALACHIANS. A CONTINUED MOISTENING OF
LOW-LEVELS IS ALSO FORECAST ALONG A PRE-FRONTAL WIND SHIFT...WHICH
MAY MAINTAIN A DRY LINE TYPE STRUCTURE FROM PARTS OF EASTERN TEXAS
NORTHWARD THROUGH EASTERN ARKANSAS AND WESTERN TENNESSEE...PERHAPS
PARTS OF WESTERN KENTUCKY. BY LATE SATURDAY AFTERNOON OR EARLY
EVENING...60F+ SURFACE DEW POINTS MAY EXTEND IN A CORRIDOR AS FAR
NORTH AS EASTERN ARKANSAS/WESTERN TENNESSEE...WITH A PLUME OF 1 INCH
PLUS PRECIPITABLE WATER AS FAR NORTH AS THE LOWER OHIO VALLEY.

...SERN PLAINS AND LWR MS VALLEY INTO THE LWR OH VALLEY...
DESPITE UNCERTAIN MID/UPPER FORCING IN THE WAKE OF THE IMPULSE
LIFTING TOWARD THE GREAT LAKES...A NUMBER OF ASPECTS APPEAR QUITE
FAVORABLE FOR SEVERE STORM DEVELOPMENT...INCLUDING THE RISK FOR
TORNADOES...SATURDAY AFTERNOON AND EVENING...PARTICULARLY ACROSS
PARTS OF EASTERN ARKANSAS INTO WESTERN TENNESSEE AND NORTHERN
MISSISSIPPI. HOWEVER...MODEL INSTABILITY FORECASTS...INCLUDING
FORECAST SOUNDINGS...CURRENTLY SUGGEST THAT THIS POTENTIAL MAY NOT
BE REALIZED. ULTIMATELY...IT MAY BE THAT A RELATIVELY COOL BOUNDARY
LAYER...WITH LOW CLOUD COVER LIMITING SURFACE HEATING...AND
RELATIVELY WARM MID-LEVELS...ALONG AND AHEAD OF THE PRE-FRONTAL WIND
SHIFT/DRY LINE...MAY PRECLUDE SUFFICIENT DESTABILIZATION. BUT AT
LEAST LOW SEVERE STORM PROBABILITIES APPEAR WARRANTED...AS THE
SEVERE RISK IS NOT COMPLETELY NEGLIGIBLE.

..KERR.. 12/13/2012

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