

000 

WWUS20 KWNS 132144

SEL6

SPC WW 132144

IAZ000-MNZ000-SDZ000-140300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 826

NWS STORM PREDICTION CENTER NORMAN OK

445 PM CDT WED AUG 13 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       SOUTHWEST MINNESOTA

       EXTREME SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 445 PM UNTIL

1000 PM 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 40

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES NORTH

NORTHWEST OF WORTHINGTON MINNESOTA TO 25 MILES EAST SOUTHEAST OF

SIOUX CITY IOWA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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 825...



DISCUSSION...A SMALL CLUSTER OF STORMS...SOME WITH SUPERCELL

STRUCTURES...SHOULD CONTINUE TO MOVE GENERALLY SWD FROM SW MN INTO

NW IA ALONG A RESIDUAL OUTFLOW BOUNDARY FROM EARLIER STORMS.  A

NARROW CORRIDOR OF MODERATE INSTABILITY /MLCAPE VALUES NEAR 2500

J/KG/ AND EFFECTIVE BULK SHEAR NEAR 35 KT WILL SUPPORT A CONTINUED

THREAT FOR LARGE HAIL AND DAMAGING WINDS.  WHILE AN ISOLATED/BRIEF

TORNADO CANNOT BE RULED OUT...RELATIVELY WEAK LOW-LEVEL SHEAR AND

MULTIPLE STORM MERGERS/INTERACTIONS WILL TEND TO LIMIT ANY SUCH

THREAT.



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 35020.





...THOMPSON

