

966 

WWUS20 KWNS 172319

SEL7

SPC WW 172319

IAZ000-MNZ000-NEZ000-SDZ000-180600-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 447

NWS STORM PREDICTION CENTER NORMAN OK

620 PM CDT WED JUN 17 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       EXTREME SOUTHWEST MINNESOTA

       NORTHEAST NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 620 PM

UNTIL 100 AM CDT.



HAIL TO 2.5 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 80

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES WEST

NORTHWEST OF ONEILL NEBRASKA TO 30 MILES SOUTHEAST OF SPENCER

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.



OTHER WATCH INFORMATION...CONTINUE...WW 439...WW 440...WW

441...WW 442...WW 443...WW 445...WW 444...WW 446...



DISCUSSION...SCATTERED SEVERE STORMS WILL FORM AND/OR MOVE INTO THE

WATCH AREA FROM THE W/SW OVER THE NEXT FEW HOURS.  STRONG

INSTABILITY IS PRESENT ACROSS THIS AREA TO THE N OF A NWD MOVING

OUTFLOW BOUNDARY ACROSS ERN NEB...WHILE DEEP LAYER VERTICAL SHEAR IS

SUFFICIENT FOR SUPERCELLS.  AN ISOLATED TORNADO MAY OCCUR...BUT

LOW-LEVEL SHEAR IS NOT PARTICULARLY STRONG WITH RELATIVELY STRAIGHT

HODOGRAPHS...THUS SUPERCELLS WITH LARGE HAIL SHOULD BE THE PRIMARY

SEVERE THREAT.  AS A FEW STORM MERGERS OCCUR...THERE WILL BE SOME

INCREASE IN THE WIND DAMAGE THREAT LATER THIS EVENING.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 27025.





...THOMPSON

