# 2021 Naperville–Woodridge tornado

On the evening of June 20, 2021, an intense tornado affected the Chicago suburbs of Naperville, Woodridge, Darien, Burr Ridge, and Willow Springs in DuPage and Cook Counties in Illinois. It was the strongest tornado spawned by a surface low over Wisconsin, which spawned a total of four tornadoes across Illinois and Indiana. The tornado, striking well after dark, was rated an EF3, reaching speeds of up to 140 mph (230 km/h), and had a path length of 14.8 mi (23.8 km) and reached a width of 600 yd (550 m), while causing 11 injuries, downing thousands of trees, and inflicting widespread property damage primarily across Naperville and Woodridge.
In the immediate aftermath, the damage was described as "extensive", with 900 properties damaged, 300 of which were considered significantly damaged, and 29 deemed uninhabitable. The non-profit Naperville Tornado Relief raised over one million dollars to aid in cleanup effort in 2023, while some repairs were still ongoing as of 2024. It was the strongest tornado in the Chicago metropolitan area since the 2015 Coal City tornado, and the first major tornado in DuPage County since the 1976 Lemont tornado.

## Meteorological synopsis

On June 20, 2021, the Storm Prediction Center had outlined an Enhanced (3/5) risk for severe weather over extreme eastern Iowa, northern Illinois and Indiana, southern Michigan, and extreme northwest Ohio for the potential of severe weather, focused on damaging straight-line winds, with the potential for isolated large hail and non-significant tornadoes. A conditional threat for the development of supercells existed over northern Illinois, with forecasters noting the difficulty of predicting any large-scale threat due to numerous existing outflow boundaries in the risk area.
Two rounds of severe weather were forecasted, with one being an afternoon mesoscale convective vortex system that had moved through Missouri, central Illinois, and northern Indiana. A second round of storms was expected to reach the Chicago metropolitan area later that evening. At 9:40 p.m. CDT, a severe thunderstorm watch was issued across most of northeastern Illinois and extreme northwestern Indiana. The main threat was clusters of storms producing severe downburst winds, with only a low (20%) risk for a tornado, and a very low (5%) chance of a significant tornado.
During the afternoon, daytime heating was impeded by cloud cover. Later on in the evening, when the cloud cover decreased, daytime heating resumed, which, along with a strong lower-level jet, rapidly destabilized the atmosphere. A surface low had developed near the border of Iowa and Minnesota, which by 10 p.m. CDT, had moved eastward to Wisconsin while deepening to 997 millibars. An observation from the National Weather Service Chicago, Illinois at Lewis University Airport, taken at around 4z (11 p.m. CDT), revealed MUCAPE values of 1556 J/kg, as well as extreme storm-relative helicity values of 644 m$^2$/s$^2$ at 0–1 kilometers and 857 m$^2$/s$^2$ at 0–3 kilometers, where storm-relative values of helicity above 150 m$^2$/s$^2$ are considered favorable for tornadogenesis. In addition to the tornado in Naperville, two others were reported near Romeoville and Addison in Illinois, and a third near South Haven, Indiana.
A tornado warning was issued for much of Kane and DuPage counties at 10:43 p.m., including Aurora, Batavia, West Chicago, and western portions of Naperville, as the National Weather Service office in Romeoville tracked two areas of rotation in the area; one over Aurora, and another near Maple Park.

## Tornado summary

The tornado first touched down at 11:02 p.m. in the Springbrook Prairie Forest Preserve, with the first tornado warning including Naperville and Woodridge issued at 11:05 p.m. for radar-indicated rotation. This warning included areas of Chicago as well, specifically the Chicago Lawn and Midway International Airport areas. Around this time, the tornado caused intense tree damage to the forest preserve before moving to the Quall Drive area at EF1 intensity. Despite causing significant tree damage, most structural damage was a result of falling trees until the tornado reached the intersection of Killdeer and Bailey, where EF1 damage to houses occurred. At 11:06 p.m., the tornado crossed the West Branch DuPage River, and at around 11:09 p.m., intensified to EF2 strength as it approached Princeton Circle in Naperville. Here, the tornado caused the collapse of a poorly-anchored house, an area of low-end EF3 damage with wind speeds estimated at 140 mph (230 km/h). This was the most intense damage produced by the tornado. The tornado maintained EF2 intensity through Woodridge.
At 11:13 p.m., the tornado crossed over Interstate 355 near Woodridge, and at 11:16 p.m., the National Weather Service upgraded the initial tornado warning to particularly dangerous situation wording, as meteorologists had confirmation that the tornado, now described as "large and extremely dangerous", was moving into Darien. The warning text also stated that "[r]adar confirms debris with this tornado moving over populated areas". Two minutes later, at 11:17 p.m., a correlation coefficient scan from the KLOT weather radar site at Lewis University Airport indicated debris lofted up to 20,000 ft (3.8 mi; 6.1 km) into the air. At this time, the tornado had weakened to EF1 intensity as it impacted Burr Ridge in Cook County, Illinois. By this point, the tornado was producing only tree damage, and lifted at 11:25 p.m. near Buffalo Woods in Willow Springs, Illinois. The tornado warning that included Cook County expired at 11:45 p.m., 20 minutes after the tornado had lifted.

## Aftermath

Less than 10 minutes after the tornado lifted, WBBM-TV, Chicago's CBS affiliate, released a news story which described "extensive" damage in Woodridge and Naperville. Daytime surveys conducted from an ABC-7 helicopter showed large trees uprooted and blown up to 40 ft (12 m).
A total of 900 structures received some form of damage, of which 300 had suffered significant damage. 29 properties across Lisle Township were declared uninhabitable. By June 2 the next year, 22 were still in varying stages of repair. On June 22, Alicia Tate-Nadeau, director of the Illinois Emergency Management Agency, toured storm damage in Naperville and Woodridge with DuPage county officials. On June 27, Brian McDaniel of the Illinois River Valley Red Cross met with county officials and opened the Multi-Agency Resource Center, where over 1,000 volunteers assisted to provide aid to those affected by the tornado. The center was opened for two days.
The non-profit group Naperville Tornado Relief was established in the aftermath of the event. They planned to raise $1.5 million to assist in cleanup of properties affected by the tornado. This goal was augmented in January 2023 by Illinois House Bill 969, which awarded the group $1 million. By May 2024, 66 yards across Naperville had been replaced by the group.
As of 2024, some repairs were still ongoing.

## Non–tornadic effects

The system brought sporadic downburst winds and rainfall. Over a 24-hour period, total rainfall amounts were reported at 2.75 in (70 mm) in Lake Zurich in Lake County, 2.62 in (67 mm) inches in Elk Grove Village in Cook County, and 2.44 in (62 mm) inches in Bartlett in DuPage County.