

000 

WWUS20 KWNS 202053

SEL3

SPC WW 202053

IAZ000-NEZ000-210300-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 623

NWS STORM PREDICTION CENTER NORMAN OK

350 PM CDT MON AUG 20 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       WEST CENTRAL AND SOUTHWEST IOWA

       CENTRAL AND EASTERN NEBRASKA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 350 PM UNTIL

1000 PM CDT.



TORNADOES...HAIL TO 3 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 90 STATUTE

MILES EAST AND WEST OF A LINE FROM 55 MILES WEST SOUTHWEST OF

BEATRICE NEBRASKA TO 40 MILES NORTHEAST OF NORFOLK NEBRASKA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU3).



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 621...WW 622...



DISCUSSION...THUNDERSTORMS ARE EXPECTED TO CONTINUE DEVELOPING

ALONG/EAST OF SURFACE TROUGH LINE MOVING EWD ACROSS CENTRAL

NEBRASKA.  AIR MASS EAST OF THE TROUGH LINE IS VERY MOIST WITH DEW

POINTS IN 70S CONTRIBUTING TO VERY UNSTABLE CONDITIONS WITH MLCAPE

OF 3000-4000 J/KG.  WIND PROFILES INCREASE AND VEER WITH HEIGHT IN

THE LOW-MID LEVELS RESULTING IN DEEP LAYER SHEAR 40-50 KT SUPPORTIVE

OF SUPERCELLS.  IN ADDITION...LOW LEVEL SRH OF 200-300 M2/S2

/ESPECIALLY OVER EXTREME ERN NEB/WRN IA WHERE WINDS REMAIN BACKED IN

ASSOCIATION WITH OLD OUTFLOW BNDRY/ AND LOW LCL HEIGHTS SUGGEST

INCREASED TORNADO POTENTIAL...WITH ADDITIONAL THREAT FOR VERY LARGE

HAIL AND DAMAGING WINDS.



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

SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

550. MEAN STORM MOTION VECTOR 26025.





...WEISS

