EF1 tornado, Greene to Rudd, Iowa, December 15, 2021

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

December 15, 2021

Touchdown

6:53 PM CST (00:53 UTC)

Lifted

6:57 PM CST (00:57 UTC)

On the ground

4 minutes

Path length

4.2 miles (6.7 km)

Path width

200 yards (183 m)

Deaths

0

Injuries

0

Property damage

$10,000

Counties

Butler and Floyd counties

Touchdown point

42.887, -92.912

Lift-off point

42.941, -92.877

Record number

2112151853-01

33 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 110 mph.

• Satellite signatures show substantial tree damage on the east side of this farmstead. Tough to gauge the full extent, but given the lack of foliage and fast storm motion, likely saw EF1 damage here.

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

December 15, 2021 was an unprecedented and historic event for the state of Iowa and the central US. It featured the first-ever December derecho observed anywhere in the United States and the first Moderate Risk of severe thunderstorms issued by the NWS Storm Prediction Center in December for Iowa. Unofficially, it set the new single-day Iowa records for the most tornadoes and the most EF-2/F-2 or stronger tornadoes since 1950. Finally, it will break the all-time December record high temperature for Iowa. ||Tornadoes: There were 63 confirmed tornadoes that occurred in Iowa, 21 of which were rated EF-2. Sixty three is unofficially the most tornadoes in Iowa in a single day with the previous being 35 tornadoes on August 31, 2014. Further, 21 EF-2 tornadoes is unofficially the most EF-2/F-2 or stronger tornadoes in a single day with the previous being 16 tornadoes on June 7, 1984. Prior to this event, a total of 5 tornadoes had occurred in Iowa in December since 1950 with all of them in southeastern Iowa. | |Thunderstorm Wind: Numerous straight line wind gusts were also associated with these thunderstorms, some in excess of 80 mph. During the event, nearly the entire state of Iowa was under a Severe Thunderstorm Warning at some point. Audubon reported the highest gust in Iowa at 88 mph. This storm also met the criteria for a ���derecho'', which makes it the first derecho on record in the month of December anywhere in the United States. Finally, we had an unofficial gust of 108 mph recorded by a mesonet station near Sheffield, Iowa associated with one of the tornadic circulations. ||Environmental Wind: After the line of storms had passed, numerous strong, non-thunderstorm wind gusts over 70 mph occurred overnight. The top three non-thunderstorm wind gusts were 83 mph in Decatur City, 81 mph in Marshalltown, and 80 mph in Johnston. The Des Moines International Airport recorded a 74 mph non-thunderstorm wind gust, which is the highest non-thunderstorm wind gust at this location since 1970.| |Temperatures: In addition to the severe weather and strong non-thunderstorm winds, the temperatures were remarkable and record setting. Numerous record daily highs were broken by many degrees. In addition and preliminarily, the all-time December record high temperature for Iowa of 74 degrees that was set in Thurman, IA on December 6, 1939 was broken with four sites reaching 75 degrees (Oskaloosa, Muscatine, Iowa City, and Ottumwa).||For detailed environmental analysis, including soundings, please view the various local NWS office event review pages: NWS Des Moines, NWS Sioux Falls, NWS Omaha, NWS Wichita, NWS Pueblo, NWS Twin Cities, NWS Quad Cities, NWS Hastings, NWS La Crosse, NWS Green Bay, or NWS Milwaukee.

An intense storm system moved across the Upper Midwest on December 15th and produced a rare severe weather outbreak across northeast Iowa. Eight tornadoes occurred across parts of Floyd, Chickasaw and Howard Counties. Four of these tornadoes were rated EF1 with one moving through Rudd (Floyd County) where the roof was removed from the library and several homes and a church were heavily damaged. The other tornadoes largely moved through rural areas damaging trees, power lines and farm buildings. In addition to the tornadoes, damaging winds occurred that blew over a semi in Floyd (Floyd County) and damaged numerous homes across the region. The Governor of Iowa declared a state of disaster emergency for Allamakee, Chickasaw, Fayette, Floyd, Howard, Mitchell and Winneshiek Counties. A federal disaster was declared for Floyd, Howard and Mitchell Counties.

This tornado was initially found using high resolution satellite imagery. The tornado developed to the southwest of the intersection of county highway C13 and T24. This tornado raced northeast and produce some minor damage before exiting into Floyd county east of county road T24 along Floyd Line Street.

This tornado formed in Butler County before crossing into southern Floyd County south of Marble Rock. The tornado remained on the ground for about 3 minutes in Floyd County as it moved across rural areas before dissipating south of Marble Rock. An NWS survey team determined this tornado to have an EF1 rating with damage limited to trees.

This tornado formed just north of Marble Rock and moved rapidly to the northeast before dissipating west of Charles City. An NWS survey team determined this tornado to have an EF1 rating. The tornado caused damage to homes, farm buildings and metal grain bins along with taking down power poles, power lines and trees.

The third tornado of the night in Floyd County formed just to the southwest of Rudd, moved northeast directly through the town and dissipated along Business U.S. Highway 18 on the north edge of town. Extensive damage occurred in the town with numerous homes sustaining damage with some roofs completely blown off. The roof of the library was removed with damage sustained to almost all the books in the building. A church on the north side of town also sustained heavy damage as did the towns water treatment plant. Water and power were not expected to be restored for several days. Classes for the Rudd-Rockford-Marble Rock school district were canceled for December 16th but the building in Rockford was open to the public for showers, warmth and served breakfast and lunch to those in need.

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

16 minutes of warning. NWS DMX issued a tornado warning for this county at 00:37 UTC, 16 minutes before the tornado touched down, in force until 00:57 UTC.

The county was under a tornado watch, issued at 19:26 UTC and running to 02:00 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 0.10 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 19:28 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.

Charles City (CCY), 29 km from the path, in the two hours either side.

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

The Des Moines radar (KDMX), 148 km away, was scanning. The volume nearest the touchdown began at 00:54 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 2021 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

124 more were confirmed in the United States that day.

All 125 of them

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.