SPC AC 220515
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1115 PM CST SAT NOV 21 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
DEEP-LAYER CYCLONE CURRENTLY OVER THE LOWER MS VALLEY IS FORECAST TO
WEAKEN THROUGH THE DAY ONE PERIOD AS IT EVOLVES INTO AN OPEN WAVE
WHILE TRANSLATING NEWD TOWARD THE MID ATLANTIC COAST. ATTENDANT
SURFACE CYCLONE WILL CONCURRENTLY WEAKEN OVER THE FAR NERN GULF OF
MEXICO BEFORE REFORMING TONIGHT OFF THE SERN ATLANTIC COAST.
PERSISTENT SURFACE RIDGING E OF THE APPALACHIANS SHOULD SUPPORT
INTENSIFICATION OF W-E ORIENTED BAROCLINIC ZONE TODAY ACROSS NRN FL
WITH ANY THREAT OF SEVERE WEATHER REMAINING CONFINED TO ALONG AND S
OF THIS BOUNDARY.
...NRN FL/SRN GA...
GRADUALLY WEAKENING SWLY LLJ WILL BE MAINTAINED AHEAD OF EJECTING
SHORT WAVE TROUGH...SUPPORTING AN INCREASE IN DEWPOINTS THROUGH THE
60S S OF FRONTAL ZONE. DESPITE THE INCREASING BOUNDARY LAYER
MOISTURE...POOR LAPSE RATES /MOST NOTABLY IN THE 700-500 MB LAYER/
WILL EFFECTIVELY LIMIT THE DEGREE OF AIR MASS DESTABILIZATION WITH
MLCAPE REMAINING GENERALLY BELOW 1000 J/KG.
TSTMS CURRENTLY IN PROGRESS OVER THE NERN GULF OF MEXICO ARE
EXPECTED TO SPREAD NEWD ACROSS THE REGION TODAY WITHIN SRN FRINGE OF
STRONGER DYNAMIC FORCING FOR ASCENT ASSOCIATED WITH DE-AMPLIFYING
MIDLEVEL WAVE. A BELT OF 45-50 KT SWLY MIDLEVEL FLOW WILL ACCOMPANY
VORTICITY MAXIMUM NEWD...EFFECTIVELY CONTRIBUTING TO AROUND 40 KT OF
DEEP-LAYER SHEAR ACROSS NRN EXTENSION OF SYSTEM WARM SECTOR. THIS
INCREASE IN VERTICAL SHEAR MAY BE SUFFICIENT TO SUPPORT EPISODIC
SUPERCELL AND/OR BOWING STRUCTURES EMBEDDED WITHIN LARGER-SCALE
CONVECTIVE SYSTEM. WHILE AN ISOLATED STRONG WIND GUST OR BRIEF
TORNADO ARE POSSIBLE...THE WEAK LAPSE RATES...MARGINAL CONVECTIVE
INSTABILITY AND OVERALL WEAKENING OF SYNOPTIC SYSTEM WITH TIME ARE
EXPECTED TO PRECLUDE A MORE ROBUST SEVERE WEATHER THREAT.
..MEAD/GRAMS.. 11/22/2009
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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