WATCHES: Severe Thunderstorm Watch Number 638

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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