Tornadoes · United States · Illinois · 2004

F0 tornado, DeKalb County, Illinois, August 24, 2004

This F0 tornado ran 2.8 miles across DeKalb County on August 24, 2004, touching down at 5:55 PM CDT and reaching 100 yards wide. It killed nobody, and did $20,000 of property damage.

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.

  1. F040 to 72 mphthis tornado

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

  2. F173 to 112 mph

    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.

The record

Rating
F0
Date
August 24, 2004
Touchdown
5:55 PM CDT (22:55 UTC)
Path length
2.8 miles (4.5 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
Property damage
$20,000
County
DeKalb County
Touchdown point
41.870, -88.650
Lift-off point
41.850, -88.630
Record number
1531

The warnings

17 minutes of warning. NWS LOT issued a tornado warning for this county at 22:38 UTC, 17 minutes before the tornado touched down, in force until 23:15 UTC.

Issued (UTC)ExpiredProductOffice
22:23 UTC23:00 UTCSevere Thunderstorm WarningLOT
22:24 UTC23:00 UTCSevere Thunderstorm WarningLOT
22:38 UTC23:15 UTCTornado WarningLOT

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 General Thunderstorms Risk. The outlook in force was issued at 19:57 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 air that afternoon

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.

Davenport, (KDVN), 12:00Z

10.9 hours before the tornado, 157 km from the path. August 24, 2004.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2004-08-24Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 221 joules per kilogram, CIN -50, lifted condensation level 613 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Davenport, at 12:00Z on 2004-08-24The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 37 square meters per square second, 0 to 6 km bulk shear 20 knots.1939Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
221 J/kg
Mixed-layer CIN
-50 J/kg
Surface CAPE
54 J/kg
Mixed-layer LCL
613 m above ground
0-6 km bulk shear
20 kt
0-1 km bulk shear
8 kt
0-1 km storm-relative helicity
37 m²/s²
0-3 km storm-relative helicity
79 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.0 K/km

Open this sounding in Storm Lab

Davenport, (KDVN), 00:00Z

1.1 hours after it, 157 km from the path. August 25, 2004.

Skew-T log-pSkew-T log-p diagram, Davenport, at 00:00Z on 2004-08-25Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 222 joules per kilogram, CIN -11, lifted condensation level 959 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Davenport, at 00:00Z on 2004-08-25The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 36 square meters per square second, 0 to 6 km bulk shear 16 knots.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
222 J/kg
Mixed-layer CIN
-11 J/kg
Surface CAPE
1457 J/kg
Mixed-layer LCL
959 m above ground
0-6 km bulk shear
16 kt
0-1 km bulk shear
6 kt
0-1 km storm-relative helicity
36 m²/s²
0-3 km storm-relative helicity
107 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.8 K/km

Open this sounding in Storm Lab

The surface observations

De Kalb (DKB), 10 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
21:05 UTC73.469.8130° 9 kt1009.8
21:25 UTC73.469.8150° 9 kt1010.2
21:45 UTC73.469.8140° 10 kt1010.2
22:05 UTC73.469.8140° 7 kt1010.2
22:25 UTC73.469.8130° 7 kt1010.2
22:45 UTC71.669.8140° 4 kt1010.2+VCTSRA
23:05 UTC69.868180° 5 kt1009.8TS
23:25 UTC71.668210° 4 kt1009.8
23:45 UTC71.668180° 3 kt1009.5
00:05 UTC71.668160° 4 kt1009.5
00:25 UTC71.669.8130° 12 kt1009.8
00:45 UTC71.668140° 12 kt1009.8

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

The radar

The Chicago radar (KLOT), 54 km away, was scanning. The volume nearest the touchdown began at 22:57 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.

This ground now

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

The other tornadoes of August 24, 2004

5 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 242:15 PM CDTF0Madison, IL1.250
August 246:00 PM EDTF0Pinellas, FL0.820$10,000
August 246:13 PM CDTF0Kane, IL0.110
August 246:21 PM CDTF0Kane, IL0.110
August 247:10 PM CDTF0McHenry, IL0.820$30,000

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.