EF0 tornado, Florence to Freeport, Illinois, August 10, 2020

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 10, 2020

Touchdown

2:12 PM CDT (19:12 UTC)

Lifted

2:17 PM CDT (19:17 UTC)

On the ground

5 minutes

Path length

4.6 miles (7.4 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

County

Stephenson County

Touchdown point

42.212, -89.688

Lift-off point

42.270, -89.645

Record number

2008101312-01

1 damage points were recorded along this path by NWS LOT, in the Damage Assessment Toolkit the survey teams carry. The highest wind the damage implies is 100 mph.

• Multiple news articles show damage to mobile homes at both mobile home parks in Forreston.

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

A powerful line of severe thunderstorms produced a derecho which tracked across eastern Iowa and northwest Illinois on the afternoon of Monday, August 10th, resulting in widespread straight line wind damage. The cost of damage from this storm was extreme, reaching an estimated 7.5 billion dollars along the path of these storms from Iowa through Illinois. Two brief tornadoes have been confirmed within the widespread swath of wind damage, one just north of the Eastern Iowa Airport in Linn County Iowa, and one just south of Freeport, Illinois. These tornadoes have been designated as EF-U, as there was no observable damage directly attributable to the tornadoes from which an EF-scale rating could be assigned. While an average of two derechos a year occur across the area, a derecho of this intensity is a roughly once-in-a-decade occurrence. Another unusual aspect of this derecho was the duration of the strong winds, with gusts over 60 mph for over an hour at some locations.||The most extreme winds, estimated at 110-140 mph, destroyed or damaged numerous outbuildings, barns, grain bins, homes, mobile homes, apartment buildings, trees, and power poles in parts of Benton, Linn, Jones, Cedar, and Clinton Counties. The Cedar Rapids area was particularly hard hit. One fatality occurred in Linn County, as a tree fell on a cyclist. Several homes, apartment complexes, and businesses sustained damage consistent with 130-140 mph winds. Radio transmission towers in Marion and Clinton, Iowa collapsed due to winds estimated around 130 mph. Wind gusts of 80-100 mph were common as the line of storms moved through the Quad Cities area and then through northwest Illinois. A small pocket of winds estimated at 100-110 mph impacted Princeton, IL in Bureau County, where a 150 foot communications tower collapsed and numerous power poles were snapped. In addition to the damage, numerous long-duration power outages occurred across the region. Damage to crops was considerable along the derecho path. Numerous semi trucks were also blown off roadways along the path of the derecho.

A tornado moved through cropland just south of Freeport. The tornado began just west of Florence, and moved N/NE for about 4.5 miles before dissipating at the southern edge of Freeport. The path was found in high resolution satellite imagery and confirmed by UAS survey. The tornado was on the leading edge of a larger swath of damaging straight line winds. There was no damage directly attributable to the tornado from which an EF-scale rating could be assigned. Thus, the tornado is designated EF-U.

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

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

The county was under a severe thunderstorm watch, issued at 16:28 UTC and running to 20:32 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 Moderate Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 15:57 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 Quad Cities radar (KDVN), 103 km away, was scanning. The volume nearest the touchdown began at 19:11 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 2020 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

26 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.