EF4 Greenfield tornado, Iowa, May 21, 2024

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 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 mphthis tornado

   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

EF4

Date

May 21, 2024

Touchdown

2:59 PM CDT (19:59 UTC)

Lifted

3:45 PM CDT (20:45 UTC)

On the ground

46 minutes

Path length

40.6 miles (65.4 km)

Path width

1,600 yards (1463 m)

Deaths

5

Injuries

35

Property damage

$32 million

Counties

Adams, Taylor and Adair counties

Touchdown point

40.900, -94.928

Lift-off point

41.328, -94.393

Record number

2405211359-01

315 damage points were recorded along this path by NWS DMX and NWS OAX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF4. The highest wind the damage implies is 185 mph.

• Trunks of large trees snapped, with some shingles removed from old house a short distance away
• Complete destruction of newly built machine shed.
• Lots of limbs broken, a few trunks snapped
• 50x80 steel frame outbuilding

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

PLEASE NOTE, for hail, wind, heavy rain and flooding, please see separate Storm Data entry for May 20-22. ||Numerous tornadoes occurred on this day with numerous injuries and four fatalities at Greenfield in Adair County.||Multiple rounds of thunderstorms brought torrential rainfall, damaging winds, hail and destructive tornadoes to the state. These thunderstorms were the result of a low pressure system which lifted north into the area on the night of May 20th, 2024, producing slow moving storms that dropped 2 to 4 inches of rainfall. This resulted in flash flooding over portions of northern and central Iowa through the morning of May 21st, 2024.||Following the heavy rainfall through the morning, skies cleared out ahead of an approaching cold front. By the afternoon hours of May 21st, 2024, this cold front produced a line of strong thunderstorms which produced multiple strong tornadoes throughout the state, including one which led to significant damage in the town of Greenfield, IA, among other locations. This line of storms also produced damaging winds, leading to widespread tree damage and power outages throughout the forecast area.

This tornado moved from Page County into Taylor County. The path was very short in Taylor County only catching the extreme northwest corner of the county. No impacts to damage indicators occurred along the path, hence the EFU rating for this portion of the path.

The tornado entered into Adams County after clipping the northwest corner of Taylor County. Damage was immediate on the county border with damage to trees and and to farm buildings and power poles within the first few miles in the county. The tornado continued to gain in strength and size as it travelled northeast through southwest Adams county remaining in rural areas south and east of Nodaway. The tornado eventually crossed Federal Highway 34 just north of Brooks with plenty of videos showing a large funnel with debris swirling below it. As the tornado crossed State Highway 148, it gained in strength with EF2 damage becoming more common. Upon reaching the intersection of 150th Street and Notchwood Avenue, EF3 damage occurred with much of an unanchored house losing walls and sliding off the foundation. All outbuildings at this site were also destroyed. As the tornado continued into the north central portion of the county, it encountered several industrial wind mills. Several of the towers collapsed along with the large blades being tossed hundreds of feet through the air. The tornado was multi-vortex at this point with a width of 1300 yards. The tornado exited the county into Adair County between Quince Avenue and Redwood Avenue. The was one death in the county from this tornado when a female driver was ejected from a vehicle which got caught within the circulation.

The tornado entered into Adams County from Montgomery County. This tornado remained in rural areas of western and northern Adams County until lifting north of the town of Carl near the Adair County line. The tornado impacted a house on the north side of 200th street shortly after entering the county removing much of the roof with general collapse of the structure. A large hog confinement facility near the intersection of 190th and Aspen was severally damage with most buildings destroyed. EF3 damage occurred to a house along 175th Street near Cherry Avenue with all wall removed except a couple of the interior walls. The outbuildings at this location were all destroyed as well. Another house along 150th Street near Dogwood Avenue had all but a few interior walls removed with EF3 damage as well. All outbuildings were destroyed at this site as well. The tornado turned slightly to the right at this point with only limited interaction with building sites but plenty of tree damage for the remainder of it path.

This large and violent tornado entered into south central Adair County from Adams County. The tornado remained a multi-vortex circulation as it moved into the county producing high end damage for much of its remaining path. The tornado encountered several houses in the vicinity of Fontanelle Road and 320th Street. Many of the structures received at least EF2 damage with one house north of the intersection receiving up to EF4 damage with a sufficiently anchored structure destroyed and slumped into a debris field nearby. Additional EF4 damage was noted at a farmstead on Jordan Avenue south of 280th Street with the house destroyed and trees chewed down to only the largest trucks and portions of the bark removed. The path then passed through another wind mill area with additional turbines collapsing west of Kent Avenue. The tornado then passed over Nodaway Park Ponds and entered the southwest side of Greenfield along SW 3rd Street. Several structures over the next several blocks had up to EF4 damage from SW 3rd Street over the SE 3rd Street and South of Linn Street and north of Oak and Noble Streets. Most of these saw complete destruction of the house with much of the debris scattered in the area but not completely swept away. The tornado weakened slightly for the later half of the destructive path through Greenfield. EF3 damage was widespread from SE Kent Street and SE 4th Street to the Intersection of E Iowa Street and NE 8th Street. The tornado exited the east side of Greenfield near the Adair County Fairgrounds. The tornado continued east northeast and gradually weakened impacting a few more houses before dissipating just south of the intersection of 220th Street and Quebec Avenue. This tornado produced at least 35 injuries in addition to 4 deaths within Greenfield. All of the deaths occurred in homes. Of note, according to media reports, a Doppler on Wheels (DOW) intercept research team measured a wind speed of just over 300 mph approximately 150 feet above ground level with this tornado.

The deaths

5 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.

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

The county was under a tornado watch, issued at 18:25 UTC and running to 22:07 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 16:40 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 Des Moines radar (KDMX), 104 km away, was scanning. The volume nearest the touchdown began at 19:56 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 2024 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

42 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.