WATCHES: Tornado Watch Number 155

WWUS20 KWNS 211932
SEL5
SPC WW 211932
SDZ000-220400-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 155
NWS STORM PREDICTION CENTER NORMAN OK
230 PM CDT SAT APR 21 2007

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

CENTRAL AND EASTERN SOUTH DAKOTA

EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 230 PM UNTIL
1100 PM CDT.

TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 60 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES NORTH NORTHEAST OF
ABERDEEN SOUTH DAKOTA TO 60 MILES SOUTH SOUTHWEST OF CHAMBERLAIN
SOUTH DAKOTA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).

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 154...

DISCUSSION...TSTMS/SUPERCELLS EXPECTED TO DEVELOP IN WW OVER THE
NEXT 2 HOURS OR SO...WITH ADDITIONAL ACTIVITY LIKELY SPREADING NE
INTO WW FROM NEB. STRENGTHENING/DECOUPLING LLJ THIS EVENING COULD
ENHANCE LOW LEVEL STORM ROTATION/TORNADO POTENTIAL AS LARGE SCALE
ASCENT INCREASES WITH APPROACH OF NM UPR VORT. IN THE
MEANTIME...AMPLE SHEAR/INSTABILITY IS IN PLACE FOR SUPERCELLS WITH
LARGE HAIL AND POSSIBLY ISOLATED TORNADOES...ONCE CAP IS BREACHED
WITH CONVERGENCE ALONG EXISTING FRONTAL SEGMENTS/OUTFLOW BOUNDARIES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 50 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 22030.

..CORFIDI

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