A thunderstorm complex moved east across southern Minnesota during the day on the 21st. The outflow boundary from the complex progressed into northern Iowa to join with a warm frontal boundary lifting north across the state.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS DMX wrote it up.
A thunderstorm complex moved east across southern Minnesota during the day on the 21st. The outflow boundary from the complex progressed into northern Iowa to join with a warm frontal boundary lifting north across the state. The airmass was very stable to the south of the boundary with temperatures in the mid 80s to low 90s, and dew point temperatures in the low 70s to near 80. CAPE values were in the 5600 J/kg range by early afternoon. A lone thunderstorm cell formed in north central Iowa just southeast of Mason City. The storm became severe and produced a tornado southeast of Rockwell. The tornado moved southeast at first while the storm intensified, then turned east as it entered Butler County. The track of the tornado was across open country and as a result there was little more than crop damage from it. Spotter and Sheriff reports indicated the tornado was on the ground intermittently. Much of the time the condensation funnel was not in clear contact with the ground, however it would appear the strength of the tornado can be inferred from the length of the track, spotter reports, and radar presentation. Speaking to trained spotters that were on the site indicated the tornado supercell was a CLOCKWISE rotating supercell.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Des Moines, IA wrote its last area forecast discussion before the first event at Jun 21, 12:45 AM CST, 11 hours 33 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 145 AM CDT FRI JUN 21 2002 SHORT TERM... MAIN CONCERNS ARE FOR INTENSIFICATION OF CONVECTION THIS MORNING, AND POSSIBLE ISOLATED SEVERE NEAR SURFACE BOUNDARY THIS AFTERNOON AND EVENING. SURFACE FRONT AT 06Z HASNT BUDGED IN LAST FEW HOURS, WITH IA ENVIRONMENTAL MESONET DEPICTING IT FROM JUST S OF KDNS THROUGH KAMW TO KCID. OUTFLOW FROM MN AND NE IA CONVECTION CONTINUES TO PROVIDE NE OR E FLOW TO REINFORCE BOUNDARY. ELEVATED CONVECTION REFIRING IN WC/NW IA INTO SD ON SOUTHERN PERIPHERY OF 850-700MB THETA-E ADVECTION. CORFIDI PROPAGATION AND 20KT 500 MB FLOW SUPPORT AN EASTERLY MOVEMENT INTO OUR NORTHERN CWA THIS MORNING. HAVE LITTLE CONFIDENCE IN MODEL SOLUTIONS FOR TODAY, ESPECIALLY THE META, SINCE IT IS NOT HANDLING CURRENT SURFACE BOUNDARY AND CONVECTION VERY WELL. WARM SECTOR AIRMASS SHOULD DESTABILIZE TODAY, WITH INCREASE IN SOUTHERLY FLOW TO FEED ONGOING STORMS THROUGH THE MORNING HOURS. INTENSIFICATION POSSIBLE LATER THIS MORNING AS HEATING COMMENCES. PWATS CONTINUE TO INCREASE CLOSER TO 2 INCHES, MAKING HEAVY RAIN A LOCALIZED THREAT. AGREE WITH SPC ON ISOLATED SUPERCELL POTENTIAL LATE TODAY ON SURFACE BOUNDARY, PARTICULARLY NW IA WHERE CAPES AND SRH CONINCIDE WELL. CANT RULE THIS OUT ALONG THE BOUNDARY IN NC IA AS MOISTURE CONVERGENCE INCREASES. ANY OUTFLOW THIS MORNING SHOULD CONTINUE TO ENHANCE LOW LEVEL TURNING OF HODOGRAPH. SHOULD STAY CAPPED AND VERY WARM IN CENTRAL AND SOUTHERN IA. MOS TEMPS LOOK OK WITH MINOR ADJUSTMENTS. LONGER TERM... WILL MAINTAIN A CHANCE OF TSRA TONIGHT IN NORTHERN IA WITH SURFACE BOUNDARY STILL WORKING N. WIDESPREAD PRECIP SHOULD BE WELL N OF IA IN ELEVATED THETA-E ADVECTION REGIME. AFTER TONIGHT, WE SHOULD REMAIN DRY THROUGH TUESDAY WITH WARM SECTOR AND 591-594 DKM 500 MB HEIGHTS IN PLACE. LOOKS LIKE A PERSISTENCE TEMP FORECAST TOO WITH JUST SLIGHT WARMING EACH DAY. UPPER 80S TO LOWER 90S BOTH SAT AND SUN LOOK FINE. WITH DEW POINTS INTO THE LOWER 70S, OVERNIGHT LOWS SHOULD STAY ON THE WARM SIDE. .DSM...NONE KULA
The Des Moines radar (KDMX), 144 km away, was scanning. The volume nearest the first event began at 18:17 UTC.
2 tornado. Local standard time, as filed.
Intermittent track. Moved into Butler County.
Intermittent track. Moved in from Cerro Gordo County.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2002Every state in 2002This day in weather historyThe tornado archive for Iowa, 2002Warnings in Iowa, June 2002
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 5294525, 5294526.