F1 tornado, Hopkins Park to Grant Park, Illinois, April 20, 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

April 20, 2004

Touchdown

7:35 PM CDT (00:35 UTC)

Path length

6.0 miles (9.7 km)

Path width

75 yards (69 m)

Deaths

0

Injuries

0

County

Kankakee County

Touchdown point

41.050, -87.950

Lift-off point

41.100, -87.850

Record number

813

The tornado began in an open field and moved north northeast along county road 11000 East, knocking down trees and limbs. The tornado intensified from County Road 2630 South to 2430 South where homes were damaged, a mobile home was destroyed and large trees were knocked down or damaged. The most intense damage occurred at a church where the roof was taken off and walls were pushed down. The tornado continued across a farm field knocking over 2 pivot irrigation systems. It ended near 1000 South where trees were damaged.

The tornado formed just southwest of the intersection of County Roads 5000S and 3000W. Eyewitnesses stated there were multiple funnels aloft occasionally lowering at this point. The developing vortex continued northeast to cross 3000S just west of 1000W. A brick one story house was directly hit. The roof was torn off and scattered northeast in a field across the street. Numerous large trees were snapped or uprooted around the home. An empty corrugated grain bin was pushed into a tree. The tornado continued northeast to the Cognis chemical plant where the brick wall of a building fell outward. About 200 feet of chain link fence was torn up. Several cinder block buildings were damaged or destroyed in this complex just northeast of where the fence was taken out. The vortex moved across railroad tracks to tear up part of the corrugated metal roofs at the River Valley Metro building (city bus storage) and other nearby businesses. The final damage was at a farm at the corner of Rts 45/52 and River Road. A barn was destroyed as well as several large sheds. The vortex apparently lifted after that as it moved just west of Kankakee Community College to the Kankakee River. Areas of debris could be seen in the trees north of River Road but no tree damage was noted.

This tornado began about 1 mile southwest of Grant Park in an open field where it was spotted by the fire department. It crossed Route 1 west of town damaging a fence. The tornado moved into town causing minor roof damage to a few homes. Part of the roof of the fire station was peeled off and a large tree fell in the yard behind the fire station. The tornado moved across an open field, then knocked down a large tree at 9000N and Route 1. There was also minor roof damage to a farm building northeast of the intersection.

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

22 minutes of warning. NWS LOT issued a tornado warning for this county at 00:13 UTC, 22 minutes before the tornado touched down, in force until 00:45 UTC.

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 General Thunderstorms Risk. The outlook in force was issued at 19:58 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.

Kankakee (IKK), 5 km from the path, in the two hours either side.

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

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 IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

31 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.