Tornado Watch 687

Issued

Sep 18, 2002, 6:00 PM CDT (23:00 UTC)

Expired

Sep 19, 2002, 12:00 AM CDT

In force

6 hr

Issued by

the Storm Prediction Center

The Omaha radar (KOAX), 84 km from the middle of the area, began a volume at 23:00 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

000 
WWUS20 KWNS 182306
SEL7  
SPC WW 182300
IAZ000-MOZ000-NEZ000-190500-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 687
STORM PREDICTION CENTER NORMAN OK
600 PM CDT WED SEP 18 2002

THE STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

   WESTERN AND CENTRAL IOWA                               
   NORTHERN MISSOURI                           
   EASTERN NEBRASKA                           

EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 600 PM
UNTIL MIDNIGHT 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 ALONG AND 85 STATUTE MILES EAST AND WEST
OF A LINE FROM 20 MILES EAST SOUTHEAST OF FALLS CITY NEBRASKA TO 30
MILES NORTHEAST OF SPENCER IOWA.

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 684...WW 685...WW 686...

DISCUSSION...LARGE SCALE ASCENT APPEARS TO BE INCREASING OVER THE
LWR MO VLY THIS EVENING...MOST LIKELY IN ADVANCE OF IMPULSE
APPARENT IN STLT IMAGERY OVER CNTRL NEB.  A VERY UNSTABLE BUT
CAPPED AIR MASS IN PLACE ACROSS WW AREA...WITH BOUNDARY LAYER DEW
POINTS IN THE UPPER 60S/LOW 70S.  AMPLE /40-50 KT/ DEEP SHEAR  
WILL BE PRESENT FOR SUPERCELLS WITH HAIL/HIGH WINDS.  WEAK LOW
LEVEL CONVERGENCE FIELDS /EXCEPT INVOF SURFACE COLD FRONT OVER ERN
NEB/...WILL ENHANCE POTENTIAL FOR A FEW STORMS TO REMAIN DISCRETE
FOR SOME TIME.  COUPLED WITH HIGH BOUNDARY LAYER MOISTURE CONTENT
...POTENTIAL WILL ALSO EXIST FOR A COUPLE TORNADOES.

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 23030.

...CORFIDI

432,0930 395,0933 395,0965 432,0962

Tornado Watches in Iowa, 2002Tornado Watches in Nebraska, 2002Tornado Watches in Missouri, 2002Every tornado watch in 2002

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.