EF1 tornado, Giard to Mc Gregor, Iowa, July 19, 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

July 19, 2017

Touchdown

6:08 PM CDT (23:08 UTC)

Lifted

6:16 PM CDT (23:16 UTC)

On the ground

8 minutes

Path length

5.8 miles (9.3 km)

Path width

400 yards (366 m)

Deaths

0

Injuries

2

Property damage

$840,000

County

Clayton County

Touchdown point

43.010, -91.283

Lift-off point

43.026, -91.171

Record number

1707191708-01

42 damage points were recorded along this path by NWS ARX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 115 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 northeast Iowa during the late afternoon of July 19th. These storms produced two tornadoes. The first, an EF-0, touched down north of Elma (Howard County) and damaged some crops. The second tornado, an EF-1, touched down west of McGregor (Clayton County) and then moved east through McGregor before dissipating over the Mississippi River. The tornado did extensive damage to the downtown area where two buildings were completely destroyed and numerous others were damaged. One person was killed in an accident cleaning up debris from the tornado when a tractor rolled and pinned the person beneath it. The storms produced a path of damaging winds from Nora Springs (Floyd County) and Mitchell (Osage County) east to Waukon (Allamakee County). Within this path, winds were estimated to range from 65 to 80 mph with numerous trees and power lines blown down. Southeast of Waukon, a barn was blown down trapping a farmer in the debris. The Governor of Iowa declared a disaster proclamation for Allamakee, Chickasaw, Clayton, Fayette, Floyd and Winneshiek Counties. The President of the United States issued a disaster declaration for Allamakee, Chickasaw, Fayette and Mitchell Counties.

An EF-1 tornado touched down about 5 miles west of McGregor and then moved through McGregor before dissipating just east of town over the Mississippi River. The most damage occurred in McGregor with two buildings downtown completely destroyed while numerous others were damaged. Two people sustained minor injuries due to flying glass. Hundreds of trees across town were snapped off. West of McGregor, the tornado damaged a storage shed, ripped back part of a metal roof from an outbuilding and damaged numerous trees. One person was killed in an accident cleaning up debris when a tractor rolled over pinning the person underneath it.

The deaths

0 direct deaths are recorded for this tornado, each with what Storm Data knows of it.

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

14 minutes of warning. NWS ARX issued a tornado warning for this county at 22:54 UTC, 14 minutes before the tornado touched down, in force until 23:18 UTC.

The county was under a severe thunderstorm watch, issued at 20:29 UTC and running to 00:46 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 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 20:01 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.

Prairie Du Chien (PDC), 8 km from the path, in the two hours either side.

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

The La Crosse radar (KARX), 90 km away, was scanning. The volume nearest the touchdown began at 23:06 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 IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

9 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.