SWODY1
SPC AC 211607
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1107 AM CDT THU MAY 21 2009
VALID 211630Z - 221200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A SUBTLE UPPER TROUGH MOVING THROUGH THE CNTRL CANADIAN PROVINCES
WILL SLOWLY MOVE EWD...GRADUALLY SHIFTING AN UPPER RIDGE JUST
OFFSHORE OF THE MID ATLANTIC EWD AS WELL. MEANWHILE AN UPPER LOW
OVER THE ERN GULF WILL SLOWLY DRIFT WWD AWAY FROM THE FL PENINSULA.
CONVERGENT BANDS ROTATING AROUND THE LOW MAY BE CONDUCIVE TO BRIEF
ROTATION. IN THE SOUTHWEST...WEAK UPPER DISTURBANCES WILL DRIFT NEWD
WITH PULSE THUNDERSTORMS AFFECTING A BROAD AREA.
...FLORIDA...
SEVERAL AREAS OF CONVERGENCE ARE NOTED ON VISIBLE SATELLITE IMAGERY
THIS MORNING...THAT WILL LIKELY PROVIDE A PRIMARY FOCUS FOR
WATERSPOUTS AND BRIEFLY ROTATING THUNDERSTORMS IN A VERY MOIST AND
UNSTABLE AIRMASS. THE MOST NOTABLE AREA OF CONVERGENCE AS OF 15Z
EXTENDS JUST OFFSHORE OF MIAMI NWWD TOWARDS TAMPA...AND MAY BE
REINFORCED BY AN OUTFLOW BOUNDARY FROM A NEARLY STATIONARY STORM
NEAR PALM BEACH. EXPECT PRIMARY THREAT TO BE OVER THE COASTAL WATERS
AND NEAR THE IMMEDIATE COAST...AS WEAK FLOW WILL BE CONDUCIVE TO
WATERSPOUTS. FARTHER N...A DIFFUSE WARM FRONT WILL DRIFT TOWARDS THE
PANHANDLE...WHILE ADDITIONAL CONVERGENT BANDS WILL ROTATE NWD AS
WELL. LOW LEVEL FLOW WILL REMAIN STRONGER ACROSS THESE AREAS...WITH
ENHANCED 0-3 KM DIRECTIONAL AND SPEED SHEAR SUPPORTING A FEW STORMS
WITH WEAK LOW LEVEL ROTATION. THIS WILL PRIMARILY BE A CONCERN BY
AFTERNOON AS THE ATMOSPHERE DESTABILIZES AND STORMS ENCOUNTER
ENHANCED BUOYANCY OF THE DIFFUSE WARM FRONT AND/OR AS LOCALIZED
CONVERGENCE AS BANDS DRIFT NWD.
...SOUTHWEST...
WEAK UPPER DISTURBANCES DRIFTING NEWD AND A MOIST/UNSTABLE AIRMASS
WILL INFLUENCE ANOTHER ROUND OF DIURNAL PULSE STORMS ACROSS A BROAD
AREA. WEAK LAPSE RATES AND UPPER FLOW SHOULD TEMPER THE SEVERE
THREAT...THOUGH ISOLD STORMS MAY BE CAPABLE OF HAIL/WIND GIVEN A
SUSTAINED UPDRAFT.
..HURLBUT/EVANS.. 05/21/2009
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