

000 

WWUS20 KWNS 212353

SEL4

SPC WW 212353

IAZ000-NEZ000-220700-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 634

NWS STORM PREDICTION CENTER NORMAN OK

650 PM CDT TUE AUG 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHERN AND WESTERN IOWA

       EASTERN NEBRASKA



EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 650 PM

UNTIL 200 AM CDT.



TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 85 STATUTE

MILES EAST AND WEST OF A LINE FROM 35 MILES NORTHEAST OF SPENCER

IOWA TO 30 MILES SOUTH OF DENISON IOWA.  FOR A COMPLETE DEPICTION

OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS

WOU4).



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 630...WW 631...WW

632...WW 633...



DISCUSSION...SCTD STRONG SUPERCELLS IN NE NEB EXPECTED TO CONTINUE

GENERALLY ESE TOWARD WRN IA LATER THIS EVENING...WITH ADDITIONAL

STORMS POSSIBLY FORMING IN ZONER OF STRENGTHENING WAA DOWNSTREAM

ACROSS NRN IA.  ACTIVITY IS ON SRN EDGE OF SEASONABLY STRONG WLY MID

LVL JET STREAK OVER CNTRL MN...AND MAY BE AIDED BY APPROACH OF JET

ENTRANCE REGION WITH THAT FEATURE LATER THIS EVENING.  COUPLED WITH

VERY RICH LOW LVL MOISTURE AND FAIRLY STEEP MID LVL LAPSE

RATES...STORMS COULD YIELD VERY LARGE HAIL/HIGH WIND AND POSSIBLE

TORNADOES.  THE ACTIVITY SHOULD CONSOLIDATE INTO ONE OR TWO

BANDS...WITH A CONTINUING THREAT FOR HIGH WIND/HAIL AND POSSIBLY A

SPIN-UP TORNADO LATER TONIGHT/EARLY WEDNESDAY.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

600. MEAN STORM MOTION VECTOR 29030.





...CORFIDI

