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WWUS20 KWNS 270539

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SPC WW 270539

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 421

NWS STORM PREDICTION CENTER NORMAN OK

1240 AM CDT SUN JUN 27 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       PART OF WEST-CENTRAL IOWA

       PART OF NORTHEAST AND EAST-CENTRAL NEBRASKA



EFFECTIVE THIS SUNDAY MORNING FROM 1240 AM UNTIL 500 AM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 45

STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES EAST

NORTHEAST OF NORFOLK NEBRASKA TO 35 MILES SOUTH SOUTHWEST OF

OMAHA NEBRASKA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



OTHER WATCH INFORMATION...CONTINUE...WW 419...WW 420...



DISCUSSION...TSTMS ARE INTENSIFYING EARLY THIS MORNING ALONG AND

AHEAD OF SFC FRONT WITHIN A VERY MOIST AND MODERATELY UNSTABLE AIR

MASS WITH MLCAPE OF 2000-2500 J/KG.  REGIONAL VWP/PROFILER DATA

INDICATE A SWLY LLJ STRENGTHENING TO 40-50 KT WHICH SHOULD MAINTAIN

AN INFLUX OF HIGH THETA-E AIR INTO GROWING STORMS.  MIDLEVEL WIND

FIELD IS NOT PARTICULARLY STRONG...BUT THE PRESENCE OF THE STRONG

LOW-LEVEL WINDS ATTENDANT TO LLJ AND DEGREE OF INSTABILITY SUGGEST

THE POTENTIAL FOR UPSCALE GROWTH INTO A DAMAGING MCS.



AVIATION...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 500. MEAN STORM

MOTION VECTOR 28030.





...MEAD

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