EF1 tornado, Irene to Garden Prairie, Illinois, April 9, 2015

1. EF065 to 85 mph

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

2. EF186 to 110 mphthis tornado

   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

EF1

Date

April 9, 2015

Touchdown

7:25 PM CDT (00:25 UTC)

Lifted

7:31 PM CDT (00:31 UTC)

On the ground

6 minutes

Path length

3.9 miles (6.3 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Property damage

$150,000

County

Boone County

Touchdown point

42.194, -88.775

Lift-off point

42.244, -88.739

Record number

1504091825-01

84 damage points were recorded along this path by NWS LOT, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF3. The highest wind the damage implies is 165 mph.

• cinder block house but no bolt all walls and debris downstream
• overview shot of path, fd1 on corner in front
• close up of foundation fd1
• all walls gone debris landed NE edge of home and spreading NE. walls only nailed in

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

Seven tornadoes were confirmed in north central Illinois in the NWS Chicago CWA. Six of the tornadoes formed from a single supercell. The atmosphere was ripe for severe weather due to highly anomalous moisture and instability for early April across the region. A strong low pressure system advanced into this favorable air mass. Combined with robust wind shear, this helped to trigger these potent storms. A long tracked violent tornado destroyed numerous homes and farmsteads along its path across north central Lee, eastern Ogle, northwest Dekalb, and southern Boone counties. This path included the far northwest side of Rochelle, Interstate-39, and a direct hit in the community of Fairdale where two fatalities occurred. This was the strongest tornado in the NWS Chicago CWA since the F5 tornado that struck Plainfield, IL on August 28th, 1990.

This is a continuation of a tornado that began in Dekalb County. This tornado was identified from a storm chaser video and survey. Three barns were destroyed on Pearl Street Road. Maximum winds speeds were estimated to be 110 mph. (Tornado 4b of 7).

This is the fourth segment of the Rochelle-Fairdale EF-4 tornado. At its strongest, peak winds were estimated to be 200 mph. The tornado entered Boone County just east of Irene Road. No damage occurred and the tornado lifted shortly after entering the county. (Tornado 2d of 7).

This was a satellite tornado that formed from the same storm that formed the long tracked EF-4 tornado. A small zoo was heavily damaged with walls collapsed on several outbuildings and small barns. Three animals were killed. Softwood trees 4 to 6 inches in diameter were snapped. The estimated peak wind was 85 mph. (Tornado 5 of 7).

Witnesses said the tornado touched down in a field then moved northeast destroying a detached garage. The tornado ripped the roof off of a home though the walls mainly remained intact. Several hardwood trees were snapped. Maximum wind speeds were estimated to be 110 mph. (Tornado 6 of 7).

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

27 minutes of warning. NWS LOT issued a tornado warning for this county at 23:58 UTC, 27 minutes before the tornado touched down, in force until 00:45 UTC.

The county was under a tornado watch, issued at 18:52 UTC and running to 01:59 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 Enhanced Risk, with a 0.10 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 20:00 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.

Rockford (RFD), 27 km from the path, in the two hours either side.

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

The Milwaukee radar (KMKX), 85 km away, was scanning. The volume nearest the touchdown began at 00:20 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

18 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.