Alert archive / Iowa / Severe Thunderstorm Watches in 2002

Severe Thunderstorm Watch 539

July 27, 200224 counties in Iowa; 7 counties in Minnesota

The Storm Prediction Center issued this severe thunderstorm watch at Jul 27, 2002, 6:45 PM CDT for 24 counties in Iowa; 7 counties in Minnesota. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Jul 27, 2002, 6:45 PM CDT (23:45 UTC)
Expired: Jul 28, 2002, 12:00 AM CDT
In force: 5 hr
Issued by: the Storm Prediction Center

All 31 counties

Allamakee County, IA, Bremer County, IA, Butler County, IA, Calhoun County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Clayton County, IA, Emmet County, IA, Fayette County, IA, Floyd County, IA, Franklin County, IA, Hamilton County, IA, Hancock County, IA, Howard County, IA, Humboldt County, IA, Kossuth County, IA, Mitchell County, IA, Palo Alto County, IA, Pocahontas County, IA, Webster County, IA, Winnebago County, IA, Winneshiek County, IA, Worth County, IA, Wright County, IA, Faribault County, MN, Fillmore County, MN, Freeborn County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Winona County, MN

Warnings issued inside it

6 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jul 27, 6:57 PM CDT	Severe Thunderstorm Warning	ARX	Mower	63 min
Jul 27, 7:19 PM CDT	Tornado Warning	ARX	Mitchell	41 min
Jul 27, 7:52 PM CDT	Severe Thunderstorm Warning	ARX	Howard	53 min
Jul 27, 8:27 PM CDT	Severe Thunderstorm Warning	DMX	Hamilton, Webster	33 min
Jul 27, 8:28 PM CDT	Tornado Warning	ARX	Winneshiek	47 min
Jul 27, 8:34 PM CDT	Tornado Warning	DMX	Webster	41 min

The nearest sounding before it

Minneapolis, MN (KMPX), launched 12:00Z, 11.8 hours before the alert went out and 180 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 485 J/kg
Mixed-layer CIN: -155 J/kg
Mixed-layer LCL: 1016 m above ground
0-6 km bulk shear: 45 kt
0-1 km storm-relative helicity: 28 m²/s²
0-3 km storm-relative helicity: 33 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.6

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

000 
WWUS20 KWNS 272345
SEL9  
SPC WW 272345
IAZ000-MNZ000-280500-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 539
STORM PREDICTION CENTER NORMAN OK
645 PM CDT SAT JUL 27 2002

THE STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

   NORTHERN IOWA                               
   SOUTHEAST MINNESOTA                          

EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 645 PM UNTIL
MIDNIGHT 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 ALONG AND 50 STATUTE MILES
NORTH AND SOUTH OF A LINE FROM 40 MILES WEST NORTHWEST OF FORT
DODGE IOWA TO 65 MILES EAST SOUTHEAST OF ROCHESTER MINNESOTA.

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 538...

DISCUSSION...THUNDERSTORMS INTENSIFYING ALONG IA/MN BORDER IN AREA
OF WEAK SURFACE CONVERGENCE.  VERY UNSTABLE AIR MASS ACROSS WW AREA
WITH CAPES TO 5000 J/KG AND MDT DEEP LAYER SHEAR SUPPORT CONTINUED
DEVELOPMENT OF STRONG/SEVERE THUNDERSTORMS E/SEWD INTO NRN IA.


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 600.  MEAN STORM
MOTION VECTOR 25030.


...HALES

432,0945 441,0911 424,0911 420,0945

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 26, 9:40 PM CDT	Severe Thunderstorm Watch	SPC	Adair, Adams, Appanoose, Benton, Black Hawk, Boone and 43 more	5 hr
Jul 27, 12:00 PM CDT	Severe Thunderstorm Watch	SPC	Anoka, Benton, Carver, Chisago, Crow Wing, Dakota and 23 more	6 hr

Nearby

Severe Thunderstorm Watches in Iowa, 2002 Severe Thunderstorm Watches in Minnesota, 2002 Every severe thunderstorm watch in 2002

Sources

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.