SWODY1
SPC AC 181240
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0640 AM CST FRI DEC 18 2009
VALID 181300Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY INTO EARLY TONIGHT FOR
THE FL PENINSULA...
...FL AREA THROUGH EARLY TONIGHT...
A SURFACE CYCLONE S OF MOB THIS MORNING WILL DEVELOP ENEWD ALONG A
BAROCLINIC ZONE ACROSS N FL THROUGH THIS EVENING...AS A SRN STREAM
SHORTWAVE TROUGH OVER THE LOWER MS VALLEY/ADJACENT N CENTRAL GULF OF
MEXICO EJECTS ENEWD IN ADVANCE OF AN AMPLIFYING NRN STREAM TROUGH
THAT WILL REACH THE MID MS VALLEY. GRADUAL PHASING WILL OCCUR LATER
TODAY THROUGH EARLY SATURDAY...WHICH WILL SUPPORT STRONG
CYCLOGENESIS JUST OFF THE COAST OF THE CAROLINAS OVERNIGHT.
MEANWHILE...THE SURFACE WARM SECTOR WILL OVERSPREAD CENTRAL/S FL AS
A RESIDUAL/WEAK FRONT ALONG THE SE FL COAST LIFTS NWD IN ADVANCE OF
THE SURFACE LOW. A TRAILING COLD FRONT WILL CROSS THE ERN GULF AND
REACH THE FL W COAST THIS EVENING...AND CONTINUE EWD ACROSS ALL OF
FL FRIDAY NIGHT.
A LOOSE BAND OF MAINLY LOW-TOPPED CONVECTION HAS PERSISTED THROUGH
THE EARLY MORNING HOURS ALONG THE WEAK BAROCLINIC ZONE FROM CAPE
CANAVERAL SWD TO PALM BEACH. RELATIVELY SHALLOW BUOYANCY AND
SOMEWHAT COOLER/MORE STABLE CONDITIONS OVER LAND HAVE LIMITED THE
SUPERCELL/TORNADO THREAT THUS FAR...THOUGH LOW-LEVEL SHEAR HAS BEEN
SUFFICIENT FOR ROTATING STORMS JUST OFFSHORE. THIS AREA OF
CONVECTION SHOULD REMAIN LARGELY OFFSHORE. HOWEVER...ANOTHER BELT
OF DEVELOPING THUNDERSTORMS WILL CONTINUE TO SPREAD NEWD FROM THE
KEYS/SE GULF ACROSS S FL THROUGH THE MORNING. A GRADUAL INCREASE IN
LOW-LEVEL AND DEEP-LAYER VERTICAL SHEAR...AND SOME LOW-LEVEL
WARMING/MOISTENING...SHOULD SUPPORT AN INCREASING THREAT FOR
SUPERCELLS AND A COUPLE OF TORNADOES ACROSS S FL THROUGH THE
MORNING/MIDDAY. THIS THREAT SHOULD ALSO SPREAD NWD TOWARD CENTRAL
AND N FL WITH THE RETREAT OF THE WEAK FRONT NOW NEAR THE
COAST...THOUGH MORE WIDESPREAD CLOUDS/RAIN MAKE DESTABILIZATION LESS
CERTAIN TOWARD N FL.
ANOTHER ROUND OF THUNDERSTORMS WILL BE POSSIBLE LATER THIS AFTERNOON
INTO EARLY TONIGHT AS THE COLD FRONT MOVES ACROSS FL FROM THE ERN
GULF OF MEXICO. LOW-LEVEL FLOW IS EXPECTED TO VEER TO SWLY IN
PROXIMITY TO THE FRONT...LEAVING MORE UNIDIRECTIONAL WIND PROFILES
AND DAMAGING GUSTS AS THE PRIMARY SEVERE THREAT BY THIS
EVENING/EARLY TONIGHT.
..THOMPSON.. 12/18/2009
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