

000 

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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