DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 200657
SWODY2
SPC AC 200655

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CST TUE NOV 20 2007

VALID 211200Z - 221200Z

..THERE IS A SLGT RISK OF SVR TSTMS CENTERED OVER THE MID SOUTH/TN
VALLEY REGION...

..SYNOPSIS...
MID-LEVEL TROUGH IS FORECAST TO INTENSIFY/EXPAND ACROSS THE U.S.
THIS PERIOD...WITH CYCLONIC FLOW FORECAST ACROSS THE ENTIRE COUNTRY
BY THE END OF THE PERIOD.

AS THIS TROUGH EXPANDS...A COLD FRONT -- INITIALLY FORECAST TO
EXTEND FROM THE LOWER GREAT LAKES REGION SWWD ACROSS THE MID MS
VALLEY AND INTO CENTRAL TX -- WILL PROGRESS STEADILY SEWD. BY THE
END OF THE PERIOD...THE BOUNDARY SHOULD EXTEND FROM NEW ENGLAND SWWD
ACROSS THE APPALACHIANS AND CENTRAL GULF COAST REGION INTO THE WRN
GULF OF MEXICO.

..OH/TN/MID AND LOWER MS VALLEYS AND CENTRAL GULF COAST REGION...
SHOWERS AND A THUNDERSTORMS SHOULD BE ONGOING AT THE START OF THE
PERIOD INVOF COLD FRONT...FROM THE GREAT LAKES REGION SWWD INTO THE
OZARKS. COMBINATION OF BOUNDARY-LAYER MOISTURE SPREADING NEWD AHEAD
OF THE FRONT AND AFTERNOON HEATING SHOULD YIELD MARGINAL
DESTABILIZATION...WITH OVERALL DEGREE OF CAPE LIMITED BY FAIRLY WEAK
LAPSE RATES. NONETHELESS...DEGREE OF INSTABILITY WILL SUPPORT AN
INCREASE IN CONVECTIVE COVERAGE AND INTENSITY THROUGH THE AFTERNOON
AND INTO THE EVENING.

WHILE SUFFICIENT FOR SOME ORGANIZATION...DEGREE OF DEEP-LAYER SHEAR
IS NOT FORECAST TO BE PARTICULARLY STRONG /AROUND 40 KT/...AS
STRONGER FLOW ALOFT SHOULD REMAIN WELL THE COOL SIDE OF THE FRONT.
HOWEVER...A FEW OF THE STRONGER/MORE PERSISTENT STORMS/LINE SEGMENTS
COULD PRODUCE LOCALLY STRONG/GUSTY WINDS AND PERHAPS SOME MARGINAL
HAIL. GREATER SEVERE THREAT -- THOUGH STILL LIMITED -- COULD PROVE
TO BE ISOLATED TORNADOES...AS SLY/SSWLY BOUNDARY-LAYER FLOW BENEATH
25 TO 35 KT WSWLY LOW-LEVEL JET ACROSS THE MID SOUTH/OH VALLEY
REGION SHOULD YIELD 20 TO 30 KT 0-1 KM SHEAR. WITH LOW CLOUD BASES
ALSO ANTICIPATED...THREAT APPEARS GREAT ENOUGH WHEN COMBINED WITH
WIND POTENTIAL TO INITIATE A SLIGHT RISK THIS FORECAST...CENTERED
OVER THE MID SOUTH/TN VALLEY REGION.

.GOSS.. 11/20/2007

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