

139 

WWUS20 KWNS 081934

SEL7

SPC WW 081934

IAZ000-MNZ000-NEZ000-SDZ000-090300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 587

NWS STORM PREDICTION CENTER NORMAN OK

235 PM CDT SUN AUG 8 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       PARTS OF NORTHERN IOWA

       PARTS OF SOUTHERN MINNESOTA

       PARTS OF NORTHEASTERN NEBRASKA

       PARTS OF SOUTHEASTERN SOUTH DAKOTA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 235 PM UNTIL

1000 PM CDT.



HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

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



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 35 MILES WEST OF

ONEILL NEBRASKA TO 30 MILES NORTH NORTHEAST OF MASON CITY IOWA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU7).



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...WITH THE AIR MASS ACROSS THE WATCH BECOMING VERY TO

EXTREMELY UNSTABLE AND GENERALLY ONLY WEAKLY CAPPED...THUNDERSTORMS

EXPECTED TO DEVELOP FROM W TO E VICINITY SURFACE BOUNDARY.  GIVEN

THE MLCAPES OF 4000 J/KG AND 30-40 KT OF SHEAR...SEVERE

THUNDERSTORMS INCLUDING LARGE HAIL AND DAMAGING WINDS ARE LIKELY.

POTENTIAL FOR ISOLATED SUPERCELLS PRIOR TO STORMS EVOLVING INTO

FORWARD PROPAGATING CLUSTERS FOR AN ENHANCED HAIL AND WIND DAMAGE

THREAT.



AVIATION...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 27025.





...HALES

