F1 tornado, Janesville, Iowa, June 1, 2001

1. F040 to 72 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. F173 to 112 mphthis tornado

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. 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.

4. 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.

5. F4207 to 260 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. 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.

7. 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.

Rating

F1

Date

June 1, 2001

Touchdown

4:12 PM CDT (21:12 UTC)

Path length

8.5 miles (13.7 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$30,000

County

Bremer County

Touchdown point

42.650, -92.470

Lift-off point

42.670, -92.330

Record number

784

A very dynamic weather situation took place over Iowa during the afternoon of the 1st. The dynamics were sufficient to overcome the shortcomings in moisture available for the system. A cold front dropped southeast out of the Dakotas into Iowa during the afternoon. Surface dew points were generally in the mid 50s ahead of the front, though a narrow ribbon of upper 50s to lower 60s was found just ahead of the front. As the cold front dropped southeast, a very strong closed low at 500 mb was also dropping into the area. This helped to destabilize the atmosphere as freezing levels fell to the 8000 to 10,000 foot range by evening. A small area of thunderstorms developed by mid day over north central Iowa. The storms intensified rapidly during the maximum heating of the day. Thunderstorms fired southwest of the original area and became severe quickly. For the most part the storms produced hail and small tornadoes. The first tornado touched in Crawford County. The county Emergency Manager reported seeing 7 funnel clouds and two brief touchdowns with the initial cell. The tornadoes were all small and were only on the ground briefly. Several other brief touchdowns occurred in the County before the storm moved east. The strongest tornado touched down on the edge of the town of Denison. A 14 x 50 metal building was destroyed. A fire hydrant was damaged in the vicinity by flying debris. It was reported that water could be seen being sucked out of the hydrant by the tornado. The tornado threat shifted into northeast Iowa for the rest of the afternoon. Several tornadoes touched down in Bremer, Butler, and Black Hawk Counties. Most of these were quite small and did little damage however. The longest track tornado touched down in the Janesville area of Bremer County and tracked over 8 miles to the east, lifting just east of the town of Denver. The countryside is quite open between these two locations. For this reason, damage was minimal as the tornado actually missed both of the towns. With the cold air aloft, hail was a significant factor. There were reports of at least half inch diameter hail with nearly all of the storms. Numerous reports of hail of an inch up to golf ball size were received. The storms produced three inch diameter hail on the north side of Belmond, causing significant damage to the area and reportedly covering the ground. One of the storms became very intense over Butler County during the early afternoon. Softball size hail was reported with this cell, causing significant damage south of the town of Allison. The storms over southwest Iowa underwent a transition into more of a wind event. High winds were reported in Cass County as the storms moved through the Griswold area. By mid afternoon, the storms in southern Iowa had taken on a bow configuration. As the storms moved through Adair County, very strong winds swept through the northeast part of the county. The winds toppled power lines northeast of Greenfield. As the storms continued east, the intensity decreased. The storms still produced gusty winds, but speeds were generally in the 45 to 55 MPH range.

Tornado swept through open countryside across Southern Bremer County. Damage was limited to mainly outbuildings and crops.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

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 Storm Prediction Center had this point in a Slight Risk. The outlook in force was issued at 20:47 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.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

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

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

The Des Moines radar (KDMX), 150 km away, was scanning. The volume nearest the touchdown began at 21:11 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.

The live radar over the trackEvery 2001 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

24 more were confirmed in the United States that day.

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.

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