Severe Thunderstorm Watch 826

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