DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180539
SWODY1
SPC AC 180538

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1138 PM CST TUE NOV 17 2009

VALID 181200Z - 191200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
LARGE UPPER LOW INITIALLY FORECAST OVER MO/IL IS FORECAST TO WEAKEN
THIS PERIOD...WHILE SHIFTING NWD UP THE MS VALLEY TO ERN IA/NRN IL
LATE. THIS PERSISTENT/INCREASINGLY-BLOCKY FLOW OVER THE ERN HALF OF
THE U.S. WILL LEAD TO WEAKENING OF THE UPSTREAM TROUGH MOVING ACROSS
THE WRN CONUS THROUGH THE PERIOD.

AT THE SURFACE...A COLD FRONT MOVING ACROSS THE WRN U.S. DURING THE
FIRST HALF OF THE PERIOD IS PROGGED TO BECOME MORE ILL-DEFINED WITH
TIME...IN CONJUNCTION WITH THE WEAKENING UPPER SYSTEM.
MEANWHILE...HIGH PRESSURE WILL GENERALLY PREVAIL ACROSS THE ERN U.S.
AS THE SURFACE LOW ASSOCIATED WITH THE UPPER SYSTEM DISSIPATES
THROUGH 19/12Z.

STRONG SELY LOW-LEVEL JET IS PROGGED OVER PARTS OF THE ERN THIRD OF
THE CONUS...PARTICULARLY FROM THE CENTRAL/SRN APPALACHIANS INTO THE
OH VALLEY/MIDWEST/UPPER GREAT LAKES REGION...AHEAD OF
VERTICALLY-STACKED UPPER SYSTEM. THIS SHOULD LEAD TO
MINIMAL/ELEVATED DESTABILIZATION...AND ASSOCIATED INCREASE IN
THUNDER POTENTIAL FROM AFTERNOON ONWARD.

ELEVATED NATURE OF THE CONVECTION AND WEAK INSTABILITY SHOULD
PRECLUDE STRONGER CONVECTION ACROSS MOST OF THIS REGION. ONE AREA
OF SLIGHTLY GREATER POTENTIAL MAY EVOLVE ACROSS THE ERN CAROLINAS.
HERE...STORMS ROOTED WITHIN THE BOUNDARY LAYER MAY EVOLVE WITH TIME.
WHILE RELATIVELY WEAK FLOW IN THE 850 TO 500 MB LAYER COMBINED WITH
VERY MODEST INSTABILITY SUGGESTS LITTLE THREAT FOR LONG-LIVED
STORMS...MODELS HINT THAT 0-1 KM SHEAR MAY BECOME SUFFICIENT FOR
WEAK LOW-LEVEL ROTATION WITH A STRONGER CELL OR TWO. ATTM...THREAT
APPEARS LOW ENOUGH TO PRECLUDE EVEN 2% TORNADO PROBABILITY...BUT WE
WILL CONTINUE TO MONITOR THIS AREA IN LATER FORECASTS.

..GOSS/JEWELL.. 11/18/2009

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