

000 

WWUS20 KWNS 182321

SEL5

SPC WW 182321

IAZ000-MNZ000-NEZ000-SDZ000-190600-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 615

NWS STORM PREDICTION CENTER NORMAN OK

615 PM CDT SAT AUG 18 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHERN IOWA

       SOUTHWEST MINNESOTA

       NORTHERN NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 615 PM

UNTIL 100 AM CDT.



TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 55 STATUTE

MILES NORTH AND SOUTH OF A LINE FROM 40 MILES SOUTH OF

CHAMBERLAIN SOUTH DAKOTA TO 20 MILES SOUTH SOUTHEAST OF MASON

CITY IOWA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



OTHER WATCH INFORMATION...CONTINUE...WW 614...



DISCUSSION...POTENTIAL SHOULD INCREASE FOR TSTMS/SUPERCELLS TO

DEVELOP ALONG STALLED SFC BOUNDARIES IN SE SD/N CNTRL NEB IN THE

NEXT COUPLE OF HOURS IN RESPONSE TO SUSTAINED HEATING/CONVERGENCE.

OTHER STORMS MAY FORM LATER THIS EVENING ALONG WARM FRONT EXTENDING

ESE INTO NRN IA AS LLJ VEERS AND STRENGTHENS.  WHILE MID LVL

TEMPERATURES ARE RATHER WARM...AND SHORTWAVE FORCING FOR ASCENT

APPEARS WEAK... BOUNDARY LAYER IS VERY WARM/MOIST.  CONSIDERABLE LOW

LVL DIRECTIONAL SHEAR IS ALSO PRESENT INVOF WARM FRONT.

THUS...POTENTIAL WILL EXIST FOR POSSIBLE TORNADOES IN ADDITION TO

SVR HAIL/WIND WITH DISCRETE STORMS THAT DO INDEED FORM.  ACTIVITY

SHOULD MERGE INTO AN MCS TONIGHT...WITH A DIMINISHING THREAT FOR

TORNADOES...BUT A LINGERING THREAT FOR HAIL/WIND.



AVIATION...TORNADOES AND 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

550. MEAN STORM MOTION VECTOR 28015.





...CORFIDI

