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942 

WWUS20 KWNS 312158

SEL8

SPC WW 312158

IAZ000-MOZ000-NEZ000-010600-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 638

NWS STORM PREDICTION CENTER NORMAN OK

500 PM CDT TUE AUG 31 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       IOWA

       NORTHWEST MISSOURI

       SOUTHEAST NEBRASKA



EFFECTIVE THIS TUESDAY AFTERNOON AND WEDNESDAY MORNING FROM 500

PM UNTIL 100 AM CDT.



HAIL TO 1.5 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 70

STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES WEST OF FALLS

CITY NEBRASKA TO 60 MILES EAST NORTHEAST OF MASON CITY IOWA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



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.



DISCUSSION...TSTMS SHOULD CONTINUE TO INCREASE IN COVERAGE AND

INTENSITY ALONG/AHEAD OF COLD FRONT THIS EVENING WITHIN A MOIST AND

MODERATE TO STRONGLY UNSTABLE WARM SECTOR WITH MLCAPE OF 2000-4000

J/KG.  APPROACH OF A LOW AMPLITUDE SHORT WAVE TROUGH AND 40-45 KT

MIDLEVEL SPEED MAX WILL SERVE TO ENHANCE BACKGROUND ASCENT AND

VERTICAL SHEAR WITH ENVIRONMENT SUPPORTIVE OF ORGANIZED MULTICELLS

AND MARGINAL SUPERCELL AND BOWING STRUCTURES.  DAMAGING WIND GUSTS

APPEAR TO BE THE PRIMARY HAZARD WITH THE MOST INTENSE STORMS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27030.





...MEAD

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