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000 

WWUS20 KWNS 190144

SEL8

SPC WW 190144

IAZ000-NEZ000-SDZ000-190900-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 538

NWS STORM PREDICTION CENTER NORMAN OK

840 PM CDT WED JUL 18 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       MUCH OF CENTRAL AND EASTERN NEBRASKA

       SOUTHEASTERN SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 840 PM

UNTIL 400 AM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 135

STATUTE MILES EAST AND WEST OF A LINE FROM 10 MILES NORTH OF

YANKTON SOUTH DAKOTA TO 30 MILES SOUTH SOUTHEAST OF NORTH PLATTE

NEBRASKA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).



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...THIS SEVERE THUNDERSTORM WATCH REPLACES

SEVERE THUNDERSTORM WATCH NUMBER 535. WATCH NUMBER 535 WILL NOT

BE IN EFFECT AFTER 840 PM CDT. CONTINUE...WW 529...WW 531...WW

532...WW 533...WW 534...WW 536...WW 537...



DISCUSSION...TSTMS/POSSIBLE SUPERCELLS EXPECTED TO INCREASE IN

COVERAGE/STRENGTH THROUGH EARLY THURSDAY AS NOCTURNAL INCREASE IN

SWLY LLJ AND LARGE SCALE ASCENT ASSOCIATED WITH APPARENT UPR IMPULSE

NOW OVER THE NEB PANHANDLE ENHANCE UVV ACROSS REGION.  VERY UNSTABLE

AIR PER 00Z LBF/OAX RAOBS...LARGE T/TD SPREADS ABOVE THE BOUNDARY

LAYER...AND RICH BOUNDARY LAYER MOISTURE SUGGEST POTENTIAL FOR A

ESE-MOVING FORWARD-PROPAGATING SYSTEM/BOW WITH HIGH WIND ACROSS

CNTRL NEB.  OTHER STORMS EXPECTED TO INCREASE ALONG ELEVATED UPLIFT

SURFACE IN SE SD.  THESE MAY BRIEFLY ROTATE AND POSE A THREAT FOR

HAIL/WIND AND PERHAPS AN ISOLATED TORNADO BEFORE MERGERS YIELD A

BROKEN LINE WITH POSSIBLE SMALLER SCALE BOWING SEGMENTS.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

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

MOTION VECTOR 30025.





...CORFIDI

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