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301 

WWUS20 KWNS 091159

SEL1

SPC WW 091159

IAZ000-NEZ000-091900-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 681

NWS STORM PREDICTION CENTER NORMAN OK

655 AM CDT SUN AUG 9 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN AND CENTRAL IOWA

       A SMALL PART OF NORTHEAST NEBRASKA



EFFECTIVE THIS SUNDAY MORNING AND AFTERNOON FROM 655 AM UNTIL 200

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 20 MILES SOUTH

SOUTHWEST OF SIOUX CITY IOWA TO 30 MILES SOUTH OF WATERLOO IOWA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU1).



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 680...



DISCUSSION...SLIGHTLY ELEVATED TSTMS/SUPERCELLS NOW IN E CNTRL NEB

MAY CONTINUE E AND POSSIBLY INTENSIFY AS THEY ENCOUNTER INCREASINGLY

SHALLOW LAYER OF POST-FRONTAL AIR E OF THE MO RVR /REF MCD 1835/.

35-40 KT ESELY CLOUD LAYER SHEAR AND DEGREE OF INSTABILITY ABOVE

SHALLOW NEAR-SFC LAYER SUGGEST POTENTIAL FOR LARGE HAIL AND...WITH

TIME... FORWARD-PROPAGATING BOWING SEGMENTS WITH HIGH WIND.  DEEP

UNIDIRECTIONAL FLOW WITH MOISTURE/INSTABILITY FEED IN THE UPWIND

DIRECTION FURTHER SUGGESTS POTENTIAL FOR BACK-BUILDING/REGENERATIVE

STORMS AFTER LEAD ACTIVITY HAS MOVED THROUGH.



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 26030.





...CORFIDI

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