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000 

WWUS20 KWNS 211526

SEL1

SPC WW 211526

FLZ000-CWZ000-220100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 551

NWS STORM PREDICTION CENTER NORMAN OK

1125 AM EDT SAT JUL 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL AND SOUTHERN FLORIDA PENINSULA

       COASTAL WATERS



EFFECTIVE THIS SATURDAY MORNING AND EVENING FROM 1125 AM UNTIL

900 PM EDT.



HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES EITHER SIDE OF A LINE FROM 25 MILES NORTH NORTHEAST

OF OCALA FLORIDA TO 40 MILES SOUTH SOUTHWEST OF MIAMI FLORIDA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU1).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



DISCUSSION...SEASONABLY COOL MID-LEVEL TEMPERATURES OF -9 TO -10 C

AT 500 MB COUPLED WITH A VERY MOIST BOUNDARY LAYER IS RESULTING IN

AN ALREADY STRONGLY UNSTABLE AIR MASS THIS MORNING WITH MLCAPES OF

3000-3500 J/KG.  VIGOROUS TSTM DEVELOPMENT IS EXPECTED ALONG

EVOLVING SEA BREEZE BOUNDARIES AS WELL AS SYNOPTIC COLD FRONT AND

PRE-FRONTAL WIND SHIFT.  WHILE VERTICAL SHEAR REMAINS QUITE

WEAK...THE DEGREE OF INSTABILITY WILL BE SUPPORTIVE OF ORGANIZED

TSTMS CAPABLE OF WET MICROBURSTS AND SOME HAIL.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 27010.





...MEAD/MCCARTHY

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