# 2024 Greenfield tornado

During the afternoon hours of May 21, 2024, a violent, long-tracked and destructive high-end EF4 tornado tracked across southwestern Iowa, devastating the city of Greenfield. The tornado, known most commonly as the Greenfield tornado, destroyed many structures and wind turbines across its path that stretched through Page, Taylor, Adams, and Adair counties, while also causing more than $31 million in property damage, killing five people and injuring 35 more. The tornado reached peak intensity within Greenfield, with National Weather Service surveyors denoting maximum wind speeds estimated at 185 mph (298 km/h). However, estimated winds of 309–318 mph (497–512 km/h) were briefly determined from inside the tornado by a Doppler on Wheels portable radar unit, one of only three times that wind speeds exceeding 300 miles per hour (480 km/h) have been determined in a tornado from radar observations.
The tornado formed amidst a week-long period of elevated tornadic activity in an area expected to be strongly conducive to the development of long-tracked and fast-moving tornadoes. Over the next 48 minutes, the tornado was observed by multiple storm chasers and research teams, who would determine the extreme wind figure from a direct radar measurement above the city of Greenfield. In addition to one fatality on a highway in Adams County, four fatalities occurred in Greenfield, with the damage in the city described as "horrific", as surveyors revealed damage consistent with a violent EF4 tornado, contradicting analysis of mobile radar data. The tornado has been noted as an important milestone in the practical efficacy of the Warn-on-Forecast system, which predicted tornadic activity in the vicinity of Greenfield about 75 minutes before the tornado reached the community. Maize crops would also start growing around Greenfield following the tornado, which was determined to be likely responsible for carrying in seeds.

## Meteorological synopsis

On May 21, a moderate risk for severe weather was issued over the states of Iowa, Missouri, Minnesota, Wisconsin, and Illinois, highlighting an elevated regional risk for tornadoes and strong wind gusts. Early on that morning, convective storms along a bow echo, a formation of storms associated with high winds, had formed along an boundary consisting of outflow from storm activity over western Nebraska. These storms were expected to move eastward through the southern third of Iowa, bringing a small risk of surface-based severe weather. To the north, a roughly west-to-east band of non-severe storms existed along a composite frontal and outflow boundary. North of this boundary existed a large area of rain showers that covered an area of dew points near 60 Fahrenheit and surface temperature in the lower 60s Fahrenheit. Dew points above 55 °F (13 °C) are typically considered more conducive to severe weather. These showers led to atmospheric stabilization, curtailing any severe risk north of the boundary. As the convection moved eastward out of the area, its severe risk was expected to lessen.
Later on that morning, a second severe weather threat developed as a large surface low-pressure trough had appeared over the Midwest, primarily centered over north-central Kansas, with a secondary and weaker low center near the tri-point of South Dakota, Iowa, and Minnesota. A warm front extended from the southern low center to the northeast through southeastern Nebraska and over southern Iowa, creating a large warm sector. A cold front anchored by the same low center extended southeast through central Kansas into the Oklahoma panhandle. The primary surface low was expected to move quickly to the northeast, moving the warm sector bounded by the warm front further north into east-central to southeastern Nebraska and west-central to southwestern Iowa, where atmospheric conditions conducive to severe weather would develop. Strong vertical ascent brought by the shortwave trough led to probable elevated thunderstorms over the central Nebraska/Kansas border, which would contribute to a surface-based storm system as they approached the Nebraska/Iowa border region. These surface-based storms were expected to develop into fast-moving supercells capable of producing severe weather hazards.
Early in the afternoon, the southern low center had moved to southeastern Nebraska. The warm front was expected to rapidly move northward ahead of the shortwave trough, which would bring higher dew points in the upper 60s Fahrenheit into much of Iowa. In conjunction with this, a large change in temperatures with altitude hallmarked by steep mid-level lapse rates, and mid-level CAPE values of 2500–3500 j/kg, a measure of atmospheric instability approximating the power thunderstorm updrafts have to rise, in addition to powerful wind fields producing elongated hodographs, a measure indicative of a shift in wind speed with height that allows the development of rotating thunderstorms, were expected to be present in the region throughout the early afternoon. These factors would result in an environment very conducive to significant and fast-moving severe thunderstorms. The storm mode was initially expected to be discrete, with fast-moving individual storms staying ahead of the cold front in the severe-conducive warm sector. These storms were expected to quickly develop the characteristics of severe supercell thunderstorms, with strong wind gusts up to 75 mph (121 km/h), very large hail up to 3 in (7.6 cm), and strong and long-lasting tornadoes all being possible hazards.
A particularly dangerous situation tornado watch was issued at 1:10 p.m. over much of Iowa and parts of surrounding states. All severe weather hazards were expected as the risk of "[s]everal tornadoes and a few intense tornadoes" would exist over a large region, including Adair County. The watch outlined a 90% chance of two or more tornadoes, with an 80% chance of one or more tornadoes significant on the Enhanced Fujita scale (EF2–EF5) within in the watch area.

## Tornado summary
### Formation through Adams County

The tornado would first touch down at the intersection of 110th Street and Vine Avenue in rural Page County, Iowa at 2:57 p.m. Central Daylight Time (UTC–5). Across Page County, damage up to EF1 intensity occurred, restricted primarily to tree branches, while the roof of a farm outbuilding was torn off. It then briefly tracked through the far northwestern tip of Taylor County, causing no damage, before moving into Adams County, where damage occurred to trees, power poles and farm buildings past the county border. The tornado intensified as it passed through rural areas to the southeast of Nodaway, before crossing U.S. Route 34 north of Brooks, where numerous videos displayed the tornado's large funnel with an area of swirling debris below. The tornado then crossed Iowa Highway 148, where 41-year-old Monica Irma Zamarron was killed after she was ejected from her vehicle after being caught in the tornado's circulation. The tornado began producing more EF2 damage past this point, before producing EF3 damage at the intersection of 150th Street and Notchwood Avenue, where an unanchored home lost its walls and slid off its foundation, while all nearby outbuildings were destroyed. Throughout the rest of Adams County, the tornado caused damage to multiple wind turbines, many of which collapsed, while reaching a maximum width in the county of 1,300 yd (1,200 m) and exhibiting multiple suction vortices each producing damage.

### Adair County

The tornado then crossed into Adair County, still with multiple-vortex characteristics, while downing a wind turbine and a metal truss tower. The tornado then approached Fontanelle Road, where a well-anchored home was destroyed with the debris thrown into a nearby field. An outbuilding on the property was completely obliterated, although the farm equipment was mostly unmoved and not severely damaged, and trees were shredded. Northeast of there on 310th Street, a nailed down cinderblock foundation home and an outbuilding were obliterated and swept away. Vehicles inside the garage of the home were damaged, but not tossed, while debris from the structures and vehicles within it were left straddling along the sides of the foundation. The tornado then moved back over open terrain, inflicting damage to an outbuilding, which was rated EF1, before downing more wind turbines. Low-end EF4 damage was observed as the tornado crossed 290th Street, where another home was leveled.
Crossing Jordan Avenue, the violent tornado leveled another home, while overturning a vehicle, and throwing another into a tree line. A nearby home was also mostly destroyed at EF3 intensity, and more trees were snapped, with several experiencing partial debarking. The tornado then moved through another wind farm, collapsing additional wind turbines. As the tornado approached Greenfield from the southwest, it tossed vehicles at EF2 intensity and destroyed two homes at EF3 intensity, with EF1 damage to roofs and outbuildings also occurring. Right before entering Greenfield, the tornado passed over Nodaway Park Ponds where two outbuildings were destroyed, and another home suffered roof damage at EF2 intensity.

#### Greenfield and dissipation

The tornado then entered the southwest part of Greenfield, and began producing EF4 damage again, reaching its peak intensity of mid-range EF4 shortly after it entered the town. Dozens of homes were leveled with some homes being partially swept away, and mobile homes and outbuildings were obliterated. The most intense damage occurred when a well-built home was obliterated and swept away. The estimated wind speed at this location was 185 mph (298 km/h). Many other homes suffered extensive roof and exterior wall damage, and many large trees were snapped and stubbed, including some that landed on and contributed to houses being leveled. The tornado then produced high-end EF3 damage to the southeast side of town, continuing to heavily damage homes, including some that were leveled or shifted off their foundations and obliterating mobile homes, as well as snapping large trees. The tornado then produced low-end EF4 damage on the eastern side of town near the intersection of Iowa 92 and Iowa 25. More homes were leveled, shifted off their foundations, or suffered severe roof and exterior wall damage. It also heavily damaged or destroyed more outbuildings and stubbed additional trees. All throughout the town, vehicles were destroyed and wooden power poles were snapped as well. Four elderly people were killed and 35 other people were injured in the town. The Adair County hospital suffered significant damage with lab and testing equipment being destroyed and hallways flooded. Catherine Hillestad, CEO of the hospital, stated that "[h]ad that tornado been any closer to our hospital or hit us directly, this entire building would be gone", referring to the fact that the hospital was very close to some of the tornado's most intense damage. The tornado was rated EF4 on the Enhanced Fujita scale with wind speeds estimated at 185 mph (298 km/h), reaching a peak width of 1,300 yards (1,200 m) along a 42.38-mile (68.20 km) path, remaining on the ground for 48 minutes. Five fatalities occurred overall, along with 35 injuries.
Another EF2 tornado would form from the same storm that produced the Greenfield tornado as it was dissipating, which would track an additional 11.87 miles (19.10 km) through northeastern Adair County.

## Observation and research
### Storm chasers and DOW observation

Storm chaser Reed Timmer captured close-range drone footage of the tornado destroying multiple wind turbines over rural Iowa. Engineer and meteorologist Timothy P. Marshall stated while analyzing footage of the storm destroying wind turbines that the way in which the storm destroyed the turbine's blades could be used as reference for a future damage indicator for the Enhanced Fujita scale. Chicago & Midwest Storm Chasers released a video of an aerial drone survey of Greenfield shortly after the tornado struck.
A research team headed by Joshua Wurman and Karen Kosiba of the Flexible Array of Radars and Mesonets research team observed the Greenfield tornado with a myriad of observational instruments. While one crew went to deploy a pod of observational instruments in the direct path of the tornado for data collection, another, operating with a Doppler on Wheels (DOW) portable radar unit arrived in Greenfield at 3:30 p.m. and stationed themselves roughly 300 yd (270 m) away from the ultimate path of the tornado around 1 mile east of the center of the community. As the tornado struck Greenfield, the DOW unit experienced wind gusts of 80 mph (130 km/h) at their point of observation, while a weaker tornado would form directly overhead the DOW vehicle operated by Kosiba. The main tornado would narrow in width on approach to Greenfield, being described as "unusually small" as it tracked through the town, and a very brief wind gust of 263–271 mph (423–436 km/h) was briefly measured at a height of 44 metres (144 ft), which translated to an instantaneous gust of 309–318 mph (497–512 km/h) when adjusted to a ground level estimation. This extreme figure likely would have been experienced for less than a second, and has been described as one of the highest wind speed figures on Earth. This was one of only three observations of wind speeds exceeding 300 mph (480 km/h) inside of a tornado, alongside the 1999 Bridge Creek–Moore tornado and the 2013 El Reno tornado. Pieter Groenemeijer, the director of the European Severe Storms Laboratory, stated in reference to the Greenfield tornado's initial DOW measurement that "[o]n the IF-scale, 250 mph measured below 60 m above ground level is IF4 on the IF-scale, 290 mph is IF5."

### Damage analysis

The most intense damage produced by the tornado was surveyed around 12:17 p.m. on May 22 by the National Weather Service office in Des Moines, Iowa, which was an engineered or well constructed residence that was destroyed with its slab swept clean. The damage was consistent with a peak wind speed of 185 miles per hour (298 km/h). After the Flexible Array of Radars and Mesonets team released their extreme wind estimate, which disagreed with their survey, Yahoo News reached out to various individuals for comment about the Enhanced Fujita scale and damage in Greenfield. Bill Gallus, a professor of meteorology at Iowa State University, stated that wind measurements are collected on very few tornadoes and are therefore too inconsistently taken to be included in the final rating. Chad Hahn, a Warning Coordination Meteorologist at National Weather Service Des Moines, stated that the damage in Greenfield did not support a rating consistent with the wind estimate, but did believe such a wind gust was possible. Jimmie Schultz, the mayor of Greenfield, stated that the wind estimate and damage surveys ignored the reality that many suffered incredible personal loss due to the tornado:
   No matter what wind speed, all that other stuff. It was a vicious tornado that come through here and a lot people(sic) lost everything. You know, I mean, a few lost their lives, but most of them lost everything.
In a presentation discussing the findings during the Greenfield event by Wurman and Kosiba, the disconnect between wind speed and ground damage was discussed, with one suggestion stating that aerial wind speeds could be disrupted by housing and other structures at ground level that could have prevented them from producing damage, in addition to the tornado's fast forward speed of 45 miles per hour (72 km/h) that caused the tornado to spend less than one minute in Greenfield.
In addition to radar data, an analysis by mechanical engineer Ethan Moriarty noted that across the street from the Adair County Memorial Hospital, the tornado ripped new concrete parking lot stop blocks from the ground, which were installed sometime after August 2023. He calculated that winds of at least 247 miles per hour (398 km/h) were needed to rip the concrete stop blocks out of the ground if they were cracked prior to being pulled up, or 283 miles per hour (455 km/h) if they were uncracked prior to being ripped out of the ground. The tornado, once nearly a mile wide at one point, had shrunk in size significantly before impacting Greenfield, with the conservation of angular momentum, a concept where rotational acceleration increases as a rotating body contracts, being a potential explanation for the tornado's intensity near the end of its life. In the conclusion of his analysis, Moriarty stated that he believed the tornado was "without question a tornado capable of EF5 damage", while stating that, had the tornado been rated on a scale other than the Enhanced Fujita scale, it may have received a higher rating.

### Warn-on-Forecast

The National Severe Storms Laboratory used the Warn-on-Forecast system, an experimental forecasting tool using models and machine learning to predict individual storms, predicted a high probability of extremely strong surface level rotation in the vicinity of Greenfield over a full hour before the tornado began. This information was shared with National Weather Service forecasters across Iowa to assist in their warning-issuing operations. Forecasters had been discussing the implications of the Warn-on-Forecast output internally around 75 minutes before the tornado struck Greenfield. Increasing meteorological lead times before the onset of severe conditions is the goal of the program which aims to reduce losses of life and economic damages from severe weather events.

## Aftermath

In the hours following the tornado, emergency personnel as well as storm chasers rushed into Greenfield to provide aid. Surrounding communities such as Red Oak quickly responded in Greenfield, with aid also coming from communities on the borders of Nebraska and Missouri. The local St. John's Catholic Church parking lot was set up as a center for volunteers. In a press conference later that day, Iowa State Patrol held a press conference in Adair County, which also included the announcements of a one-day curfew in Greenfield and the establishment of security checkpoints to get into town, with only residents being allowed to enter in the immediate aftermath. Volunteers from the Y'all Squad, a non-profit established by YouTube meteorologist Ryan Hall, Y'all, entered Greenfield to assist immediate recovery efforts hours after the tornado. Hall's audience also raised $93,000 in recovery funds in the hours after the storm.
The tornado's damage scar through Greenfield was visible on satellite imagery. Governor of Iowa Kim Reynolds toured the damage the following day, describing the views as "horrific". Reynolds stated that personnel from FEMA were in Greenfield, who would be coordinating local and state recovery personnel. Due to timely response, 50% of the town's power was restored by Thursday morning. FEMA administrator Deanne Criswell, who had been working with a team in Minden, another rural Iowa community that was impacted by an EF3 tornado weeks prior, visited Greenfield on May 23 alongside Reynolds to assess damage and determine whether or not the area qualified for federal assistance, with Reynolds submitting an application for an expedited presidential disaster declaration the day prior. On May 24, president Joe Biden approved Reynolds' request for federal assistance and issued a major disaster declaration for Adair County and other counties that had experienced severe weather on May 21.
A resident of Greenfield went viral after a news clip circulated of him being distraught over losing golf clubs. In response, he received new golf clubs from Callaway and TaylorMade, and he also received an invitation to play in the John Deere Classic mini Pro-Am.
Maize began growing in Greenfield and surrounding areas in the months following the tornado. This was attributed to the tornado carrying seeds into the town, some of which may have come from grain silos, with heavy rain following the tornado also contributing to the volunteer, or naturally planted, crop's growth. The tornado struck during the time of year when maize seeds are typically planted. Many likely failed to germinate before the tornado struck, before being pulled out from the ground and brought to Greenfield.
The RAGBRAI bicycle tour stopped in Greenfield on July 23, 2024. The Greenfield Chamber of Commerce estimated that participants in the tour had raised between $50,000–60,000 in funds that would go towards tornado recovery.
By November 2024, six months following the tornado, the Greater Greenfield Community Foundation, a group intending to assist residents of the city recover, had raised a total of $1 million. Jeremy Cooper, the emergency manager of Adair County, stated that 51 building permits had been issued, with 34 homes under active construction.

### Fatalities

| Name | Age | Type of structure | Location | Additional notes |
| Monica Irma Zamarron | 49 | Motor vehicle | Iowa Highway 148 in Adams County | Initial reports stated that Zamarron may have been a storm chaser, but this was later rebuked by a family member. |
| William Williamson | 70 | Permanent home | South 5th Street in Greenfield | Williamson was rescued from his home but died of his injuries. One of Williamson's two dogs also died. |
| Michael Jensen | 73 | Permanent home | Southeast Jackson Street in Greenfield | |
| Pamela Wiggins | 77 | Permanent home | 800 block of Iowa Street in Greenfield | Pamela and Dean Wiggins were a married couple that died when the tornado struck their home north of the hospital in Greenfield. |
| Dean Wiggins | 78 | Permanent home | 800 block of Iowa Street in Greenfield | Pamela and Dean Wiggins were a married couple that died when the tornado struck their home north of the hospital in Greenfield. |