EF1 tornado, Belvidere Arpt to Chemung, Illinois, May 17, 2017

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

May 17, 2017

Touchdown

10:21 PM CDT (03:21 UTC)

Lifted

10:34 PM CDT (03:34 UTC)

On the ground

13 minutes

Path length

10.3 miles (16.6 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$100,000

Counties

Boone and McHenry counties

Touchdown point

42.334, -88.822

Lift-off point

42.438, -88.677

Record number

1705172121-01

14 damage points were recorded along this path by NWS MKX, in the Damage Assessment Toolkit the survey teams carry. The highest wind the damage implies is 70 mph.

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

A line of severe thunderstorms moved across northern Illinois late in the evening of May 17th and overnight into the early morning of May 18th. There were numerous reports of damaging winds occurring with these thunderstorms along with a few reports of hail up to the size of golf balls. An EF-1 Tornado also occurred touching down approximately two miles south of Poplar Grove and dissipating approximately 3 miles northwest of Harvard.

A tornado touched down approximately two miles south of Poplar Grove. Tree branches were broken on Poplar Grove Road where the tornado touched down. A large softwood tree trunk was snapped on Beaver Road. Trees were debarked on Beaverton Road. A small outbuilding was destroyed on Edson Road. Hardwood trees were snapped at the trunk on Russellville Road and again on Capron Road. On the east side of Capron, A garage was destroyed and shingles were peeled off the north side of a home and dozens of trees were snapped. Another small outbuilding was destroyed on County Line Road with debris strewn about three quarters of a mile downstream. The tornado passed into McHenry County on County Line Road south of Hunter Road.

This is a continuation of a tornado that began in Boone County two miles south of Poplar Grove. The tornado crossed into McHenry County south of Hunter Road. Softwood trees were snapped on Hunter Road. Hardwood trees were snapped or sheared on White Oaks Road.

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

17 minutes of warning. NWS LOT issued a tornado warning for this county at 03:04 UTC, 17 minutes before the tornado touched down, in force until 03:30 UTC.

The county was under a tornado watch, issued at 20:44 UTC and running to 04:26 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 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 00:57 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 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 Milwaukee radar (KMKX), 67 km away, was scanning. The volume nearest the touchdown began at 03:19 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 2017 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

15 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.