F1 tornado, Clark Mills, Wisconsin, July 13, 2004

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

July 13, 2004

Touchdown

3:40 PM CDT (20:40 UTC)

Path length

4.2 miles (6.8 km)

Path width

500 yards (457 m)

Deaths

0

Injuries

0

Property damage

$1.6 million

County

Manitowoc County

Touchdown point

44.100, -87.880

Lift-off point

44.050, -87.830

Record number

360

Thunderstorms developed in moist and unstable air as a cold front and upper level trough moved through northeast Wisconsin. Several severe thunderstorms formed during the afternoon, one of which produced a tornado in the vicinity of a lake breeze front in Manitowoc county. Strong winds from these storms downed trees and power lines in Valders (Manitowoc co.), near Wild Rose (Waushara co.), and from Athelstane to Middle Inlet (Marinette co.) and damaged trees at a country club in Luxemburg (Kewaunee co.) and at Whitefish Dunes State Park (Door co.). Tennis ball size hail fell between Reedsville and Whitelaw (Manitowoc co.) and golf ball size hail was reported at Lakewood (Oconto co.). There were also several reports of quarter size hail.Law enforcement officers watch as two funnel clouds moved across central Manitowoc county. One of the funnels touched down near Clarks Mills causing extensive damage to two farms. The tornado destroyed 2 garages, 2 barns, 2 milking parlors, 3 silos, 45 calf hutches and about 80 acres of alfalfa. It damaged barns, service buildings, farm equipment and at least a dozen residences, one of which was uninhabitable. The tornado snapped and uprooted trees and carried a calf about half a mile away where it was found still alive.

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 Moderate Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 20:08 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.

The Green Bay radar (KGRB), 51 km away, was scanning. The volume nearest the touchdown began at 20:37 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.

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

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

The live radar over the trackEvery 2004 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

5 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.