Tornadoes · United States · Iowa · 2004

F0 tornado, Black Hawk County, Iowa, May 21, 2004

Name: F0 tornado, Black Hawk County, Iowa, May 21, 2004
Start: 2004-05-21T20:21:00.000Z
Location: Black Hawk County, Iowa

This F0 tornado ran 0.3 miles across Black Hawk County on May 21, 2004, touching down at 3:21 PM CDT and reaching 30 yards wide. It killed nobody.

The rating scale

Tracks are drawn in the color of the rating. The Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

F040 to 72 mphthis tornado
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
F173 to 112 mph
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
F2113 to 157 mph
Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.
F3158 to 206 mph
Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.
F4207 to 260 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
F5261 to 318 mph
Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.
Unrated
The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

The record

Rating: F0
Date: May 21, 2004
Touchdown: 3:21 PM CDT (20:21 UTC)
Path length: 0.3 miles (0.5 km)
Path width: 30 yards (27 m)
Deaths: 0
Injuries: 0
County: Black Hawk County
Touchdown point: 42.450, -92.350
Lift-off point: 42.450, -92.350
Record number: 901

The warnings

38 minutes of warning. NWS DMX issued a tornado warning for this county at 19:43 UTC, 38 minutes before the tornado touched down, in force until 20:40 UTC.

Issued (UTC)	Expired	Product	Office
19:43 UTC	20:40 UTC	Tornado Warning	DMX
20:35 UTC	21:15 UTC	Tornado Warning	DMX
20:38 UTC	22:45 UTC	Flash Flood Warning	DMX

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The forecast that day

The Storm Prediction Center had this point in a Moderate Risk, with a 0.15 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 20:02 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

What forecasters said that day

The local office's own words before the tornado touched down, 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 tornado touched down at May 21, 5:15 AM CDT, 10 hours 6 minutes earlier.

Area forecast discussion, May 21, 5:15 AM CDT, 10 hours 6 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
515 AM CDT FRI MAY 21 2004

.DISCUSSION...
FORECAST CONCERNS INCLUDE CONVECTIVE TRENDS AND HEAVY RAIN POTENTIAL
THROUGH THE WEEKEND. FAVORED GFS GIVEN INTIALIZATION PROBLEMS OF ETA
AS OF LATE. FRONTAL BOUNDARY CURRENTLY WORKING ITS WAY BACK NORTH
INTO CENTRAL IOWA AS HEAVY RAIN PRODUCING THUNDERSTORMS TRACK
THROUGH NORTH CENTRAL IOWA. THE MOST INTENSE CELL PRODUCED SEVERE
WIND GUST IN FRANKLIN COUNTY AROUND 430 AM. THE BOUNDARY WILL
PROVIDE THE FOCUS FOR CONTINUED LOCALLY HEAVY RAIN AND THE THREAT OF
SEVERE WEATHER THROUGH THE WEEKEND. THE GFS PERSISTS IN FOCUSING ON
AREAS NORTH OF INTERSTATE 80 FOR HEAVY RAINS...WITH 1-3 AND LOCALLY
HIGHER AMOUNTS POSSIBLE. WILL HOLD OFF ON FLOOD WATCH ATTM DUE TO
UNCERTAINTIES WITH FRONTAL PLACEMENT...BUT WILL FINE TUNE HYDROLOGIC
OUTLOOK TO FAVOR AREAS NORTH OF HIGHWAY 20 FOR POTENTIAL RIVER
FLOODING AND FLASH FLOODING. AFTER A BRIEF BREAK SUNDAY NIGHT INTO
EARLY MONDAY...ACTIVE WEATHER WILL RESUME LATER MONDAY INTO TUESDAY
WITH ANOTHER FRONT THROUGH THE REGION.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

KINNEY

Hazardous weather outlook, May 21, 6:49 AM CDT, 8 hours 32 minutes before

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
649 AM CDT FRI MAY 21 2004

IAZ004>007-015>017-023>028-033>039-221100-
BLACK HAWK-BREMER-BUTLER-CALHOUN-CERRO GORDO-EMMET-FRANKLIN-GRUNDY-
HAMILTON-HANCOCK-HARDIN-HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-SAC-
WEBSTER-WINNEBAGO-WORTH-WRIGHT-
649 AM CDT FRI MAY 21 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHERN IOWA...NORTH OF THE
HIGHWAY 30 CORRIDOR.

.DAY ONE...TODAY AND TONIGHT

SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND
TONIGHT...WITH DAMAGING STRAIGHT LINE WINDS AND LARGE HAIL
POSSIBLE. LOCALLY HEAVY RAINFALL AMOUNTS FROM 1 TO 3 INCHES ARE ALSO
EXPECTED...AND COULD PRODUCE FLASH FLOODING ACROSS AREAS THAT
RECEIVED SUBSTANTIAL RAINFALL LAST EVENING AND OVERNIGHT...MAINLY
ALONG AND NORTH OF HIGHWAY 20.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A RISK OF ISOLATED SEVERE STORMS SATURDAY AND SATURDAY
NIGHT...AND AGAIN SUNDAY AND MONDAY. A BIGGER THREAT...HOWEVER WILL
BE FLASH FLOOD PRODUCING RAINS...ESPECIALLY SATURDAY AND SATURDAY
NIGHT.

.SPOTTER ACTIVATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED LATER THIS AFTERNOON AND
TONIGHT. SPOTTER ACTIVATION MAY ALSO BE NEEDED AT VARIOUS TIMES
THROUGH MONDAY NIGHT.

IAZ044>050-057>062-070>075-081>086-092>097-221100-
ADAIR-ADAMS-APPANOOSE-AUDUBON-BOONE-CARROLL-CASS-CLARKE-CRAWFORD-
DALLAS-DAVIS-DECATUR-GREENE-GUTHRIE-JASPER-LUCAS-MADISON-MAHASKA-
MARION-MARSHALL-MONROE-POLK-POWESHIEK-RINGGOLD-STORY-TAMA-TAYLOR-
UNION-WAPELLO-WARREN-WAYNE-
649 AM CDT FRI MAY 21 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL AND SOUTHERN IOWA...
ALONG AND SOUTH OF THE HIGHWAY 30 CORRIDOR.

.DAY ONE...TODAY AND TONIGHT

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND
TONIGHT...WITH DAMAGING STRAIGHT LINE WINDS AND LARGE HAIL
POSSIBLE. HEAVIER RAINFALL AMOUNTS ARE EXPECTED TO STAY TO THE
NORTH. HOWEVER...ISOLATED FLASH FLOODING IS NOT OUT OF THE
QUESTION...ACROSS AREAS THAT RECEIVED HEAVY RAIN RECENTLY...ALONG AND
SOUTH OF A LINE FROM AUDUBON...TO WINTERSET...TO OTTUMWA.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A RISK OF SEVERE STORMS SATURDAY AND SATURDAY
NIGHT...AND AGAIN SUNDAY AND MONDAY. ISOLATED FLASH FLOODING IS ALSO
POSSIBLE THROUGH THE PERIOD.

.SPOTTER ACTIVATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THIS AFTERNOON AND TONIGHT. SPOTTER
ACTIVATION MAY ALSO BE NEEDED AT VARIOUS TIMES THROUGH MONDAY NIGHT.

KINNEY

In the hours before

Local storm report, May 21, 2:56 PM CDT, 25 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
256 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0250 PM     HAIL             ALDEN                   42.51N 93.38W
05/21/2004  1.00 INCH        HARDIN             IA   TRAINED SPOTTER

&&

REESE

Local storm report, May 21, 3:06 PM CDT, 15 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
306 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0253 PM     HAIL             2 NW DIKE               42.48N 92.66W
05/21/2004  1.75 INCH        GRUNDY             IA   LAW ENFORCEMENT

&&

REESE

Local storm report, May 21, 3:10 PM CDT, 11 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
310 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0306 PM     HAIL             GRUNDY CENTER           42.36N 92.77W
05/21/2004  0.88 INCH        GRUNDY             IA   TRAINED SPOTTER

&&

REESE

Local storm report, May 21, 3:12 PM CDT, 9 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
312 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0300 PM     HAIL             ALDEN                   42.51N 93.38W
05/21/2004  1.00 INCH        HARDIN             IA   LAW ENFORCEMENT

&&

REESE

Local storm report, May 21, 3:17 PM CDT, 4 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
317 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0316 PM     HAIL             TRAER                   42.19N 92.46W
05/21/2004  1.00 INCH        TAMA               IA   LAW ENFORCEMENT

&&

REESE

Local storm report, May 21, 3:20 PM CDT, 1 minute before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
320 PM CDT FRI MAY 21 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

0315 PM     HAIL             TRAER                   42.19N 92.46W
05/21/2004  1.25 INCH        TAMA               IA   TRAINED SPOTTER

&&

REESE

The surface observations

Waterloo (ALO), 12 km from the path, in the two hours either side.

Time (UTC)	Temp (°F)	Dew point (°F)	Wind	Gust (kt)	Pressure (mb)	Weather
18:54 UTC	75	63	140° 13 kt		1009.8
19:54 UTC	73	65	70° 9 kt		1009.1	-TSRA
20:54 UTC	63	62	70° 17 kt	22	1008.1	-TSRA BR
21:54 UTC	66	62	150° 12 kt		1007.8

From the Iowa Environmental Mesonet's archive of airport observations.

The radar

The Des Moines radar (KDMX), 139 km away, was scanning. The volume nearest the touchdown began at 20:23 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)	Report	Where	County	Remark
18:52 UTC	HAIL 0.88	Steamboat Rock	Hardin, IA	REPORTED BY TRAINED SPOTTER.
19:28 UTC	TORNADO	2 W Holland	Grundy, IA
19:32 UTC	TORNADO	1 E Holland	Grundy, IA	CORRECTION ON LOCATION...ORIGINAL REPORT HAD 3 WEST OF HOLLAND AND IT SHOULD BE 1 EAST OF HOLLAND.
19:32 UTC	TORNADO	3 W Holland	Grundy, IA
19:38 UTC	TORNADO	3 N Grundy Center	Grundy, IA	TORNADO CROSSING HIGHWAY 14 WITH DEBRIS. STATE PATROL REPORT.
19:42 UTC	HAIL 0.88	Dike	Grundy, IA
19:42 UTC	TORNADO	4 Ne Grundy Center	Grundy, IA	STATE PATROL REPORT OF TWO SIMULATNEOUS TORNADOES.
19:49 UTC	TORNADO	7 Sw Dike	Grundy, IA	MOVING NORTHEAST TOWARD DIKE.
19:53 UTC	HAIL 1.75	2 Nw Dike	Grundy, IA
20:06 UTC	HAIL 0.88	Grundy Center	Grundy, IA
20:15 UTC	HAIL 1.25	Traer	Tama, IA
20:15 UTC	TORNADO	10 W Grundy Center	Grundy, IA	ON STATE HIGHWAY 175
20:16 UTC	HAIL 1	Traer	Tama, IA
20:17 UTC	HAIL 1	Dike	Grundy, IA
20:21 UTC	HAIL 1	Waterloo	Black Hawk, IA	NICKEL TO QUARTER SIZED HAIL REPORTED BY TRAINED SPOTTER.
20:21 UTC	HAIL 1	Waterloo	Black Hawk, IA
20:21 UTC	TORNADO	3 S Waterloo	Black Hawk, IA
20:22 UTC	TORNADO	5 Nw Grundy Center	Grundy, IA
20:30 UTC	HAIL 1.75	Waterloo	Black Hawk, IA
20:33 UTC	TSTM WND GST 60	4 Nw Cedar Falls	Black Hawk, IA
20:35 UTC	TSTM WND DMG	Evansdale	Black Hawk, IA	TREES DOWN ON LAFAYETTE ST.
20:41 UTC	HAIL 0.88	Waterloo	Black Hawk, IA
20:42 UTC	HAIL 1.75	Grundy Center	Grundy, IA	HIGHWAY 175 WEST OF GRUNDY CENTER
20:45 UTC	HAIL 0.88	1 Se Raymond	Black Hawk, IA
20:45 UTC	HAIL 0.88	4 Se Waterloo	Black Hawk, IA	ESTIMATED 4 MI SE OF WATERLOO, MM65, I380
21:04 UTC	HAIL 0.75	Waterloo	Black Hawk, IA
21:10 UTC	TSTM WND DMG	2 N Traer	Tama, IA	NUMEROUS TREES DOWN 1-2 MI NORTH OF TRAER
21:16 UTC	HAIL 1	Traer	Tama, IA
21:20 UTC	HAIL 0.88	2 Nw Dysart	Tama, IA
21:23 UTC	TSTM WND GST 60	3 N Clutier	Tama, IA
22:57 UTC	HAIL 1	2 E Plainfield	Bremer, IA	DELAYED REPORT.
23:00 UTC	HAIL 0.75	1 Ssw Grundy Center	Grundy, IA
23:02 UTC	HAIL 1.75	Grundy Center	Grundy, IA	WEST SIDE OF CITY.
23:09 UTC	HAIL 1	2 E Plainfield	Bremer, IA

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the track Every 2004 tornado in Iowa Every tornado in Iowa since 1950 Warnings in force in Iowa now The forecast where you are

The other tornadoes of May 21, 2004

23 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Injuries	Damage
May 21	2:28 PM CDT	F0	Grundy, IA	3.0	50
May 21	2:38 PM CDT	F1	Grundy, IA	3.5	100		$2,000
May 21	2:49 PM CDT	F0	Grundy, IA	0.5	30
May 21	4:02 PM EDT	F0	Richland, OH	0.0	0
May 21	3:15 PM CDT	F0	Grundy, IA	0.5	40
May 21	3:22 PM CDT	F0	Grundy, IA	0.5	40
May 21	4:05 PM CDT	F0	Benton, IA	0.1	50
May 21	4:07 PM CDT	F0	Benton, IA	0.1	50
May 21	4:13 PM CDT	F1	Benton, IA	1.7	150		$50,000
May 21	4:22 PM CDT	F3	Linn, IA	3.0	200		$250,000
May 21	4:44 PM CDT	F0	Benton, IA	0.0	50
May 21	5:06 PM CDT	F1	Jones, IA	6.0	100		$40,000
May 21	5:12 PM CDT	F1	Clay, IA	1.0	200		$230,000
May 21	6:00 PM CDT	F1	Pocahontas, IA	5.0	300		$30,000
May 21	6:08 PM CDT	F2	Pocahontas, IA	12.5	880	15	$2.5 million
May 21	4:16 PM PDT	F0	Spokane, WA	0.2	70
May 21	7:30 PM CDT	F0	Wright, IA	0.2	25
May 21	9:14 PM EDT	F0	Berkeley, WV	3.0	1
May 21	8:20 PM CDT	F1	Pierce, NE	1.5	150
May 21	8:44 PM CDT	F0	Brown, NE	0.2	20
May 21	9:20 PM CDT	F1	Wayne, NE	0.5	150
May 21	9:20 PM CDT	F0	Yankton, SD	0.1	50
May 21	10:13 PM CDT	F0	Garfield, NE	0.2	20

What this means

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

Sources

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.