Destructive outbreak of 12 tornadoes striking the state of Wisconsin on July 18, 1996
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The 1996 Oakfield tornado outbreak was a severe weather event that occurred on July 18, 1996, in Wisconsin, United States, primarily affecting the village of Oakfield. The outbreak produced 12 tornadoes, with the most significant being an F5 tornado which caused severe damage to the village and the surrounding areas. As of the present, this remains the most recent EF/F5 tornado to have occurred in the United States outside the peak months of April and May. No deaths were associated with the outbreak, with 17 injuries in total.
The most intense tornado of the outbreak initially touched down at 6:05p.m. CST (00:05UTC) 4 miles northwest of Oakfield, before rapidly intensifying to F5 strength just east of the village. Estimated wind speeds reached 265 mph (426 km/h) in the tornado's core as it carved a path approximately 20 miles (32 km) long. Destruction in Oakfield included leveling homes, sending vehicles airborne, bending steel rebar, and sweeping crop fields clean. The Oakfield tornado remains one of the costliest tornadoes in the state's history, with the estimated damage costs at US$40 million.
Meteorological synopsis.
On July 18, 1996, the meteorological conditions leading to the Oakfield tornado outbreak were influenced by the presence of a nearby shifting weather boundary, known as a baroclinic zone. This boundary generated strong cyclonic rotation around a surface low-pressure center over Minnesota. Warm and moisture-laden air from the Gulf of Mexico flowed northward into the Upper Midwest due to a dominant southerly wind pattern. Strong fronts displayed frontogenetic behavior, with frontogenesis at 850 hPa level curving from the border of South Dakota and Nebraska to Wisconsin, leading to strong ascent in the warm sector of the surface low-pressure system.
Despite these conditions, no severe storms occurred in the morning hours. This was because of a high convective inhibition (CIN) value caused by the presence of an elevated mixed layer (EML) and a 550 hPa inversion, which made it difficult for convection to break through. Additionally, the effects of daytime heating had not yet weakened the inversion. As the day progressed, daytime heating and evolving atmospheric conditions allowed the cap to be broken and provided the necessary ingredients for the development of the severe weather outbreak, including the devastating F5 Oakfield tornado.
By 3:33 PM CST, the National Weather Service in Milwaukee/Sullivan saw the potential for severe weather, including tornadoes, and issued the first tornado watch which covered a majority of Wisconsin, followed by a second at 6:47 PM.
Aftermath.
Following the tornado outbreak, Wisconsin Governor Tommy Thompson declared a state of emergency for Fond du Lac County, resulting in the deployment of the National Guard to aid victims and clear debris. In total, 47 of 320 homes were destroyed and 56 homes were heavily damaged, along with numerous businesses and churches. Damage estimates reached over US$40.4 million, marking the outbreak the costliest in state history.
Despite the severity of the F5 tornado and the extensive destruction it caused, no fatalities were reported, and a total of 17 people were injured during the outbreak. In the time that followed, the community of Oakfield received significant financial support from individuals and businesses in the form of donations and loans to aid in the rebuilding process. Much of the area's tree canopy and ecological landscape were devastated by the tornado, but through the concerted efforts of area residents and fundraising initiatives, over $102,000 was raised, and more than 1,400 trees were planted.
The 25th anniversary of the tornado was observed on July 18, 2021, with a series of commemorative events being held, including a parade, an outdoor church service, village-wide open houses, and a display of photographs and first-hand accounts of the tornado at the Oakfield Public Library's story walk in Acorn Park.
Notes.
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References.
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