SWODY1
SPC AC 181954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0154 PM CST SAT DEC 18 2010
VALID 182000Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...S FL...
HAVE REDUCED THE SIZE OF THE LOW-END THREAT AREA ACROSS S FL...AS
THE MAIN BAND OF CONVECTION ASSOCIATED WITH THE PASSING UPPER VORT
MAX APPROACHES THE ATLANTIC COAST. UNTIL THE CONVECTION CLEARS THE
COAST...A VERY LOW-END RISK FOR AN ISOLATED DAMAGING WIND GUST OR
BRIEF WATERSPOUT/TORNADO PERSISTS.
...PAC NW COAST...
HAVE REMOVED THAT LOW-PROBABILITY HAIL THREAT THIS FORECAST...AS
LACK OF CAPE SHOULD HINDER POTENTIAL FOR ANY MORE THAN SMALL HAIL.
OTHERWISE...POTENTIAL FOR AN ISOLATED DAMAGING GUST AND/OR BRIEF
TORNADO REMAINS NON-ZERO THIS AFTERNOON AND EARLY EVENING.
..GOSS.. 12/18/2010
.PREV DISCUSSION... /ISSUED 1027 AM CST SAT DEC 18 2010/
...S FL THIS AFTERNOON...
A LEAD SHORTWAVE TROUGH IS MOVING EWD FROM THE SE GULF OF MEXICO TO
S FL...IN ADVANCE OF THE PRIMARY WAVE OVER THE LOWER MS VALLEY. AT
THE SURFACE...A WEAK LOW W OF SRQ/FMY WILL PROGRESS EWD TO NEAR LAKE
OKEECHOBEE LATER THIS AFTERNOON AND OFF THE FL E COAST BY LATE
EVENING. GRADUAL MOISTENING OF THE WARM SECTOR AND LIMITED SURFACE
HEATING ACROSS SE FL HAVE CONTRIBUTED TO MLCAPE OF 500-1000 J/KG IN
ADVANCE OF THE ONGOING CONVECTION APPROACHING THE FL KEYS. THIS
CONVECTION WILL PERSIST THROUGH THE AFTERNOON...WITH THE POTENTIAL
FOR ADDITIONAL STORM DEVELOPMENT NEAR THE SE FL COAST WITHIN THE
PRIMARY MOISTURE PLUME. THE COMBINATION OF WEAK BUOYANCY AND
EFFECTIVE BULK SHEAR OF 30-40 KT WILL SUPPORT A FEW STORMS WITH
EMBEDDED BOW/SUPERCELL STRUCTURES...AND AN ATTENDANT RISK FOR STRONG
WIND GUSTS AND PERHAPS A BRIEF TORNADO. HOWEVER...THE OVERALL
SEVERE STORM RISK WILL BE TEMPERED BY POOR MIDLEVEL LAPSE RATES AND
MODEST LOW-LEVEL SHEAR.
...NRN CA/ORE COASTS TODAY...
A BAND OF THUNDERSTORMS IS SPREADING INLAND OVER THE ORE COAST IN
ASSOCIATION WITH AN EMBEDDED SHORTWAVE TROUGH. SATELLITE IMAGERY
CONFIRMS AN EXPANSE OF CELLULAR CONVECTION EXTENDING OFFSHORE IN THE
POST-FRONTAL ENVIRONMENT ON THE CYCLONIC SIDE OF THE MID-UPPER JET
WHERE LOW-MIDLEVEL LAPSE RATES ARE STEEP. THE THREAT FOR ADDITIONAL
THUNDERSTORMS WILL PERSIST THROUGH THE PERIOD NEAR THE COAST IN THE
ONSHORE FLOW REGIME...AIDED BY THE APPROACH OF ADDITIONAL/SUBTLE
SPEED MAXIMA. WEAK SURFACE-BASED INSTABILITY AND CLOCKWISE TURNING
HODOGRAPHS WITH HEIGHT SUGGEST SOME POTENTIAL FOR LOW-TOPPED
ROTATING STORMS...ESPECIALLY WHERE LOCAL TERRAIN MAINTAINS MORE SLY
NEAR-SURFACE WINDS. AN ISOLATED STRONG/DAMAGING GUST AND/OR BRIEF
TORNADO CANNOT BE RULED OUT. ADDITIONALLY...STEEP LAPSE RATES AND
COLD MIDLEVEL TEMPERATURES COULD SUPPORT HAIL FORMATION IN THE
STRONGER UPDRAFTS.
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