WATCHES: Tornado Watch Number 91

WWUS20 KWNS 281929
SEL1
SPC WW 281929
ALZ000-ILZ000-KYZ000-TNZ000-290200-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 91
NWS STORM PREDICTION CENTER NORMAN OK
220 PM CDT SAT MAR 28 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

NORTHERN ALABAMA
EXTREME SOUTHEAST ILLINOIS
PARTS OF WESTERN AND CENTRAL KENTUCKY
MIDDLE TENNESSEE

EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 220 PM UNTIL
900 PM CDT.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 65 STATUTE
MILES EAST AND WEST OF A LINE FROM 75 MILES NORTH OF FORT
CAMPBELL KENTUCKY TO 30 MILES SOUTH SOUTHEAST OF HUNTSVILLE
ALABAMA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND 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.

OTHER WATCH INFORMATION...CONTINUE...WW 89...WW 90...

DISCUSSION...SURFACE HEATING HAS RESULTED IN DESTABILIZATION IN
ADVANCE OF A SURFACE COLD FRONT NOW MOVING EWD ACROSS WRN TN/MS...TO
THE SE OF THE SYNOPTIC CYCLONE APPROACHING SE MO AND S OF A WARM
FRONT LIFTING SLOWLY NWD TOWARD THE OH RIVER. THUNDERSTORM
DEVELOPMENT WILL BECOME MORE PROBABLE IN THE NEXT FEW HOURS AS
MLCAPE INCREASES TO THE 500-1000 J/KG RANGE AND CONVECTIVE
INHIBITION WEAKENS. AT THE SAME TIME...STRONG DEEP LAYER VERTICAL
WILL BE MAINTAINED OVER THE WARM SECTOR ON THE NOSE OF THE 80 KT MID
LEVEL JET...AND LOW-LEVEL HODOGRAPH CURVATURE WILL BE FAVORABLE FOR
RIGHT-MOVING SUPERCELLS. THE COMBINATION OF MODEST INSTABILITY AND
STRONG VERTICAL SHEAR APPEARS FAVORABLE FOR A BROKEN BAND OF
SUPERCELLS CAPABLE OF PRODUCING A FEW TORNADOES...ALONG WITH LARGE
HAIL AND DAMAGING WINDS. THE SEVERE THREAT SHOULD INCREASE THROUGH
THE AFTERNOON...AND THEN GRADUALLY DIMINISH AFTER SUNSET AS THE
BOUNDARY LAYER STABILIZES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 24040.

...THOMPSON

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