Winterset tornado

On March 4, the Storm Prediction Center (SPC) outlined a slight risk outlook for severe weather for a negatively tilted shortwave trough positioned over the High Plains. The outlook included the possibility of strong winds, large hail, and a 5 percent chance for tornadoes, mostly throughout southern Iowa. The following day, the SPC updated the outlook to include an enhanced risk that was centered in Iowa. The probabilities for damaging winds were increased to 30 percent, and the probabilities for tornadoes were elevated to a 10 percent, unhatched area (indicating a <10% chance of EF2 or stronger tornadoes) centered along southwestern Iowa. The outlook referenced an increase in destabilization, coupled with a modest low level jet at around 40–50 kn (46–58 mph; 74–93 km/h), in an area with moderate dew points, at around 50–55 °F (10–13 °C).^[2] At noon, the SPC issued its first tornado watch, for southern Iowa and northwestern Missouri, discussing the moderate probabilities for tornadoes to occur, although a major tornado outbreak was not expected.^[3]

The tornado first touched down near the intersection of Deer Run Avenue and 280th Street to the north of Macksburg. Moving northeast, the tornado began to rapidly intensify while tracking through mainly open farmland, patches of forest, and Pammel State Park. The tornado then approached and crossed Highway 169 near the southwestern outskirts of Winterset, reaching EF4 intensity with estimated winds of 170 miles per hour (270 km/h) as it moved along Carver Road.^[4][5] A swath of EF4 damage occurred in this area as several homes were leveled or swept from their foundations. Six people who lived on Carver Road, including four members of the Bolger family, were killed. Several other people were injured in this area as well.^[6][7][8] Multiple other houses along Carver Road suffered major structural damage ranging from EF2 to EF3 in intensity, with loss of roofs and exterior walls observed.^[4] Cars were flipped and thrown, outbuildings were obliterated, debris was strewn long distances, and many large trees were snapped and denuded in this area as well.^[9]

After the large and destructive tornado exited the Winterset area, it continued to the northeast and passed through rural areas near Patterson, exhibiting a multi-vortex structure but causing little damage as moved through sparsely populated areas. Northeast of Patterson, the tornado produced low-end EF2 damage as it snapped hardwood trees along Highway 35. The tornado was estimated to have peak windspeeds of 112 miles per hour (180 km/h) in this area.^[4]

The tornado maintained low-end EF2 strength as it entered the southeastern fringes of the Des Moines metropolitan area, moving through the outskirts of Norwalk. Several businesses and other buildings in the Norwalk area suffered heavy roof damage, the Norwalk Public Works building had its garage doors blown in, a barn was destroyed, and multiple power poles were snapped in this area.^[10][4] The tornado then produced damage ranging from EF1 to mid-EF2 in intensity as it impacted portions of Avon and Pleasant Hill. Multiple houses in this area were heavily damaged, a few of which sustained roof loss. Outbuildings and garages were destroyed, many trees and power poles were snapped, and a MidAmerican Energy Company building suffered damage to its roof and garage doors. Continuing to the northeast at EF2 strength, the tornado became increasingly rain-wrapped as it tracked through rural areas to the south of Mitchellville. Numerous power poles were downed along this segment of the path, large farm buildings and barns were destroyed, and a two-story farm house had its entire roof torn off. Beyond this area, mainly low-end EF2 damage was observed as the tornado passed south of Colfax, snapping more power poles and destroying numerous barns and outbuildings. It then weakened to EF1 intensity as it moved through Lambs Grove and the north side of Newton.^[4] Damage in Newton consisted of downed trees, damage to a baseball field, and minor to moderate structural damage. Northeast of Newton, the TPI Composites manufacturing plant had a large portion of its roof torn off at the end of the damage path shortly before the tornado dissipated.^[9][11] At least five people were injured.^[12] This tornado became the first EF4 tornado to occur in Iowa since October 4, 2013, was the deadliest tornado in Iowa since May 25, 2008, and the longest tracked tornado in Iowa since April 27, 2014.^[13]

50 homes were damaged in the area, with 35 or 40 sustaining major damage. A total of seven fatalities were recorded, with two of them being children.^[14] Four of these fatalities were members of the Bolger family, who were killed when the tornado directly impacted the home that they were sheltering in; several more in the house were seriously injured.^[15][16]

• 2008 Parkersburg–New Hartford tornado – an EF5 tornado that struck Iowa nearly 14 years earlier