SWODY2
SPC AC 131729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CST THU DEC 13 2007
VALID 141200Z - 151200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
THE SPLIT BELT OF POLAR WESTERLIES EMANATING FROM THE NORTHERN
PACIFIC WILL REMAIN PROMINENT TO MUCH OF THE U.S. THROUGH THIS
FORECAST PERIOD. MODELS SUGGEST THAT PHASING OF ITS TWO PRIMARY
BRANCHES...AND ASSOCIATED EMBEDDED SHORT WAVE IMPULSES...WITH
ANOTHER STREAM EMANATING FROM THE SUBTROPICAL PACIFIC...WILL OCCUR
LATER TONIGHT INTO EARLY FRIDAY. AND...THIS IS EXPECTED TO LEAD TO
THE EVOLUTION OF AN AMPLIFIED UPPER TROUGH OVER THE INTERMOUNTAIN
WEST/ROCKIES...WHICH IS PROGGED TO DIG THROUGH THE CENTRAL/SOUTHERN
PLAINS/RIO GRANDE VALLEY BY 12Z SATURDAY. WEAK SURFACE CYCLOGENESIS
IS FORECAST TO ACCOMPANY THE DEVELOPING UPPER SYSTEM...TO THE LEE OF
THE SOUTHERN ROCKIES EARLY FRIDAY...AND ALONG A DEVELOPING FRONT
ACROSS SOUTHEAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY...FRIDAY
NIGHT INTO EARLY SATURDAY.
MODELS INDICATE THAT THE PATTERN WILL REMAIN PROGRESSIVE...WITH
ANOTHER VIGOROUS SHORT WAVE TROUGH LIKELY SWEEPING INTO THE PACIFIC
NORTHWEST COAST BY 12Z SATURDAY...WITH YET ANOTHER CLOSELY ON ITS
HEELS. SHORT WAVE RIDGING IS PROGGED TO TEMPORARILY OVERSPREAD
AREAS EAST OF THE MISSISSIPPI VALLEY THROUGH THE ATLANTIC
SEABOARD...BUT THE SUBTROPICAL HIGH CENTER TO THE EAST OF THE
BAHAMAS IS FORECAST TO CONTINUE SLOWLY WEAKENING.
..SOUTH CENTRAL STATES...
THE EVOLVING PATTERN SHOULD BE ACCOMPANIED BY INCREASING LARGE SCALE
LIFT...ASSOCIATED WITH WARM ADVECTION...AND A MODEST RETURN FLOW OF
MOISTURE OFF THE WESTERN GULF OF MEXICO...THROUGH THE
SOUTHERN/CENTRAL PLAINS AND LOWER MISSISSIPPI VALLEY. MODELS ARE
SUGGESTIVE THAT THIS WILL LEAD TO DESTABILIZATION. BUT...THIS IS
EXPECTED TO REMAIN WEAK...AND BASED ABOVE A LINGERING SURFACE OR
NEAR SURFACE INVERSION LAYER...FROM PARTS OF CENTRAL/EASTERN TEXAS
INTO UPPER PARTS OF THE LOWER MISSISSIPPI VALLEY...AND PERHAPS AS
FAR SOUTH AS MID/UPPER TEXAS COASTAL AREAS. SO...WHILE
THUNDERSTORMS APPEAR PROBABLE FRIDAY NIGHT WITH FRONTAL FORCING AND
SURFACE WAVE DEVELOPMENT...THE SEVERE POTENTIAL STILL APPEARS
NEGLIGIBLE.
..FLORIDA PENINSULA...
LOW-LEVEL MOISTENING AND WEAKENING INHIBITION AROUND THE WESTERN
PERIPHERY OF THE WEAKENING/RETREATING SUBTROPICAL RIDGE FRIDAY WILL
CONTRIBUTE TO AN INCREASINGLY FAVORABLE ENVIRONMENT FOR THUNDERSTORM
ACTIVITY...PARTICULARLY NEAR CENTRAL/SOUTHERN COASTAL AREAS.
..PACIFIC NORTHWEST...
MODELS INDICATE STRONG MID-LEVEL FORCING FOR UPWARD VERTICAL
MOTION...AND COOLING...WITH A 500 MB COLD CORE AROUND -30C...
PROGRESSING INTO THE NORTHERN CASCADES LATE FRIDAY NIGHT THROUGH
EARLY SATURDAY. IN CONJUNCTION WITH A MOISTENING ONSHORE
FLOW...THIS MAY CONTRIBUTE TO A FEW THUNDERSTORMS BY THE END OF THE
FORECAST PERIOD.
.KERR.. 12/13/2007
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