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WWUS20 KWNS 221612

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SPC WW 221612

IAZ000-MNZ000-NEZ000-SDZ000-222300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 680

NWS STORM PREDICTION CENTER NORMAN OK

1110 AM CDT WED SEP 22 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       SOUTHWEST MINNESOTA

       NORTHEAST NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY MORNING AND EVENING FROM 1110 AM UNTIL

600 PM 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 65

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

YANKTON SOUTH DAKOTA TO 25 MILES EAST NORTHEAST OF FAIRMONT

MINNESOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).



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...THE COMBINATION OF ENEWD-PROGRESSING MIDLEVEL IMPULSE

AND AN INFLUX OF A WARM/MOIST AIR MASS ALONG 40-50 KT LLJ SHOULD

SUSTAIN ELEVATED SEVERE TSTMS THROUGH THE DAY TO THE N OF SURFACE

WARM FRONT.  STEEP MIDLEVEL LAPSE RATES...MUCAPE OF 2000-3000 J/KG

AND 45-55 KT OF EFFECTIVE BULK SHEAR WILL BE MORE THAN SUFFICIENT

FOR SUPERCELLS CAPABLE OF MAINLY LARGE HAIL.



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 500. MEAN STORM

MOTION VECTOR 25030.





...MEAD

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