Draft:2024 Greenfield tornado

During the afternoon of May 21, 2024, a long-tracked and destructive tornado struck Greenfield, IA. The tornado was the strongest of a widespread tornado outbreak sequence in the Central and Southern United States between May 19–27, 2024, as well as the strongest tornado since the 2023 Rolling Fork tornado. The tornado carved a path of devastation through the southern end of Greenfield, and killed 5, four of which were in Greenfield proper.

Meteorological synopsis
On May 21, the SPC issued a moderate risk of severe weather in the states following the continuation of a strong storm system over much of the contiguous United States. The risk, which outlined large portions of Iowa, Missouri, Minnesota, Wisconsin, and Illinois, included a 15% risk for significant tornadoes. Upper-air soundings observed steep lapse rates in the middle troposphere over parts of Kansas and Missouri on the morning of May 21. The SPC predicted that these conditions would spread into the primary severe weather risk area, overlapping with a moist airmass with dew points approaching 70 F and leading to strong potential atmospheric instability. That morning, an organized cluster of thunderstorms moved into Iowa after having produced severe wind gusts in central and eastern Nebraska. This line of storms continued across central and eastern Iowa just north of a warm front, presenting a continued threat for damaging wind gusts. Additional storms began to develop along the border between Kansas and Nebraska ahead of an approaching trough. The SPC anticipated that the atmospheric environment over eastern Nebraska and western Iowa would become increasingly conducive for further organization of these storms into supercells. A tornado watch was issued by the SPC for areas near and along the Nebraska–Iowa border region at 11:10 a.m. CDT in anticipation of these changes. At 1:10 p.m. CDT, the SPC issued a tornado watch flagged as a particularly dangerous situation for much of Iowa and parts of surrounding states, including an 80% likelihood of a significant tornado occurring within the watch area. Supercells were active over southwestern Iowa by the mid-afternoon, approaching an environment favorable for tornadogenesis leading into the Des Moines area.

Storm development
In the late morning, storms started forming in eastern Nebraska. A tornado watch was issued shortly after. These storms moved east, becoming tornadic just before crossing into Iowa. As the storms moved east, a PDS tornado watch was issued for many towns, including Greenfield.

Formation and initial track
The vortex first touched down near the town of Villisca in Page County and moved northeastward at EF1 intensity, destroying all but one wall of an outbuilding and damaging the roof of a home. It then clipped the far northwestern tip of Taylor County before moving into Adams County. Continuing northeastward, the tornado reached EF1 intensity again as it approached and passed southeast of Nodaway, snapping wooden power poles, heavily damaging or destroying outbuildings, causing minor damage to homes, and snapping trees. Continuing northeastward, the tornado passed just west of Brooks, destroying and throwing a grain bin before and damaging trees.

Crossing US 34 west of Corning and continuing northeastward, the tornado heavily damaged or destroyed outbuildings, inflicted roof damage to homes, and snapped trees. The first area of severe damage occurred north of Corning as the tornado crossed Iowa 148. An outbuilding was obliterated and swept away and part of a home collapsed. This damage was rated low-end EF2. A woman driving on Iowa 148 died when she was ejected from her car after it was lofted by the tornado. The tornado continued northeastward over rural, open terrain, with the only damage being to the roofs of an outbuilding and a home. The next area of concentrated damage was at the intersection of 150th Street and Notchwood Avenue. The tornado was at high-end EF3 intensity here and a cinderblock home was completely leveled with the debris collapsing into the basement. Outbuildings on the property were destroyed, a loaded grain bin had its top ripped off, a tractor-trailer was lofted and turned 360°, and trees were snapped. To the northeast of here, the tornado continued over open terrain. EF2 damage was inflicted to a large metal outbuilding that lost its roof with EF1 roof damage to a home along with a destroyed outbuilding. It also toppled at least five wind turbines along this portion of the track, including one turbine that caught on fire, but no rating was given to this damage. The tornado exhibited violent motion and multiple vortices along this segment of the path as well.

The tornado then crossed into Adair County, where it initially uprooted trees at EF1 intensity. A home further to the northeast suffered roof and siding damage and had a snapped tree fall on it. A silo was toppled and an outbuilding was damaged as well. After toppling another wind turbine, the tornado began to cause EF2 damage, knocking down a metal transmission tower, and destroying an outbuilding. The tornado then quickly became violent and reached low-end EF4 intensity for the first time, leveling an outbuilding and a home each along Fontanelle Road and 310th Street. The tornado then moved back over open terrain with damage limited to an outbuilding. Low-end EF4 damage was observed again as the tornado crossed Jordan Avenue, where another home was leveled. A nearby home was also mostly destroyed at EF3 intensity and trees were snapped, including some that had partial debarking. As the tornado approached Greenfield from the southwest, it inflicted EF1 roof damage to a home, destroyed and outbuilding at EF2 intensity, and destroyed two homes at high-end EF3 intensity with the first one being leveled.

Greenfield
The tornado then turned east-northeastward and entered the southwest part of Greenfield, crossing onto Southwest 3rd Steet, where multiple rows of homes were destroyed, with a few swept off their foundations. Damage here was rated EF2-EF3 due to poor construction. The tornado then became violent again just beyond this point. Similar damage was inflicted throughout residential areas in southern portions of the town, including one well-built home along Southwest Oak Street which was completely destroyed, leading to an EF4 rating. It then reached its peak intensity of mid-range EF4 as it moved near the center of town, leveling and partially sweeping away dozens of homes. The vortex was now exhibiting a very tight gradient of wind, with fully destroyed homes observed next to minimally damaged structures. On the eastern side of town near the intersection of Iowa 92 and Iowa 25, the tornado inflicted severe EF2-EF3 damage to more homes, including some that were leveled or shifted off their foundations, and outbuildings were heavily damaged or destroyed.

Multiple businesses on the east side of town were damaged or destroyed. A car service station was completely swept away, with large equipment lofted off their bolting, and a separate car wash was completely flattened. The local fire department on East Iowa Street was partially damaged, as well as the local Hospital, however both facilities remained operational. Along with the destroyed homes, vehicles were destroyed, trees were stubbed, and wooden power poles were snapped throughout the town as well. Four fatalities and 35 injuries were reported in the town. As the tornado moved through the town, a Doppler on Wheels measured winds of at least > 250 mph (400 km/h), "possibly as high as 290 mph (470 km/h)" at 48 yards (44 m) above the surface. Pieter Groenemeijer, the director of the European Severe Storms Laboratory noted that "on the IF-scale, 250 mph measured below 60 m above ground level is IF4 on the IF-scale, 290 mph is IF5."

Further track and dissipation
After exiting Greenfield, the tornado moved east-northeastward for multiple miles, crossing directly over homes on Orange Ave and Pinewood Ave. The tornado finally dissipated over Quebec Ave in open terrain.

In total, the tornado traveled 43 mi, killing 5 people and injuring at least 35 others.

Aftermath
In the following hours of 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. The local St. John’s Catholic Church parking lot was set up as a center for volunteers. Iowa state governor Kim Reynolds toured the damage the following day, describing the views as "horrific." Due to timely response, 50% of the town's power was restored by Thursday morning.

A resident of Greenfield went viral after a news clip circulated of his 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.

Doppler radar findings
In following days after the tornado, researchers at the DOW (Doppler On Wheels) Facility analyzed and processed data from an associated mobile doppler radar that measured the tornado in the town. The DOW scanned over Greenfield at heights of about 30-50 m (100-160 feet ) above the ground every 7 seconds, measuring Doppler velocities up to 309-318 mph. After publishing the data, discussion was ignited over if the Greenfield tornado was now the strongest measured tornado ever recorded.