EF0 tornado, Cornell to Ocoya, Illinois, August 18, 2015

1. EF065 to 85 mphthis tornado

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

2. EF186 to 110 mph

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

3. EF2111 to 135 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. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

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

6. EF5over 200 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

EF0

Date

August 18, 2015

Touchdown

4:32 PM CDT (21:32 UTC)

Lifted

4:33 PM CDT (21:33 UTC)

On the ground

1 minutes

Path length

0.0 miles (0.0 km)

Path width

25 yards (23 m)

Deaths

0

Injuries

0

County

Livingston County

Touchdown point

40.980, -88.720

Lift-off point

40.980, -88.720

Record number

1508181532-01

Isolated supercell thunderstorms developed during the late afternoon over Livingston and McLean counties and tracked northeast toward the Chicago metro through the early evening. There were two separate and brief EF-0 tornado touchdowns in Livingston County: one near Cornell and the other north of Chenoa. No damage was observed with these brief touchdowns. The supercell thunderstorm that produced a brief EF-0 tornado near Cornell maintained persistent rotation as it tracked across Grundy County, with numerous photos of a very low wall cloud, and reports of possible brief funnel clouds at times near Kinsman and Mazon.||A line of strong to severe storms producing torrential rainfall moved in behind the supercell thunderstorms, producing sporadic wind damage in portions of northern Illinois and also flash flooding in portions of Rockford. Two additional EF-0 tornadoes associated with rotation embedded within the line of storms were confirmed: the first from extreme southeast Naperville to far eastern Woodridge, and the second a brief path through Downers Grove.||The 2.87 of rain that fell at Rockford Airport on August 18th set a new record for the date, breaking the previous record set in 2005.

A brief touchdown was reported by law enforcement. No damage occurred.

Trained spotter observed tornado just west of I-55. No damage occurred.

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

14 minutes of warning. NWS LOT issued a tornado warning for this county at 21:18 UTC, 14 minutes before the tornado touched down, in force until 22:00 UTC.

The county was under a tornado watch, issued at 18:35 UTC and running to 01:23 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 Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 20:37 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.

Pontiac (PNT), 10 km from the path, in the two hours either side.

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

The Chicago radar (KLOT), 87 km away, was scanning. The volume nearest the touchdown began at 21:34 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 2015 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

8 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.