Illinois experiences significant tornado activity, positioning the state as one of the most active in the United States outside of the traditional Great Plains. The state is located on the northern edge of “Dixie Alley,” a region seeing an increasing frequency of severe weather events. Historically, Illinois has been the site of devastating tornado events, highlighting the persistent threat these storms pose across the region.
When Tornadoes Strike Illinois
The atmospheric dynamics that produce tornadoes are a regular occurrence across Illinois, with the state averaging between 50 and 54 tornadoes annually. The peak season for these storms typically runs from April through June, accounting for the majority of the state’s yearly total. During this primary period, the greatest frequency of tornadoes tends to occur during the late afternoon and early evening hours, generally between 3 p.m. and 7 p.m.
This seasonal peak is driven by the regular clash of two distinct air masses over the Midwest. Warm, moisture-rich air flowing northward from the Gulf of Mexico meets cooler, drier air moving in from the northern or western parts of the continent. This interaction creates the atmospheric instability and wind shear necessary for the formation of supercell thunderstorms, the type that often produce tornadoes.
While spring and early summer are the most active periods, tornadoes can occur in Illinois during any month of the year. The state also experiences a secondary peak of activity in the fall and early winter. This non-traditional season can produce strong tornadoes, highlighting the need for year-round vigilance regarding severe weather.
The strength of these rotating columns of air is measured using the Enhanced Fujita (EF) Scale, which assigns a rating from EF0 (weakest) to EF5 (strongest) based on the damage observed. The majority of Illinois tornadoes are on the lower end of this scale. However, the state has experienced violent, high-end EF4 and EF5 storms that have caused extensive destruction.
Geographic Concentration Within the State
Tornadoes have touched down in every county across Illinois, confirming that the entire state is susceptible to the hazard. However, patterns of occurrence indicate that certain regions experience a higher concentration of activity than others. Central Illinois, a region characterized by its flat topography, tends to see the highest overall density of tornado touchdowns.
The northern and central parts of the state generally record more events than the southern region, though the southern counties have historically been impacted by some of the most destructive storms. When accounting for the differences in county size, counties in the central and eastern portions, such as Ford, Saline, and Lake (Illinois), often show higher rates of tornado incidence per land area.
Proximity to major metropolitan areas, such as the greater Chicago area, means that even less frequent events can have a higher impact on public safety. Cook County, which encompasses much of Chicago, has recorded one of the highest raw counts of tornadoes due to its immense size and population density. Storms like the 1990 Plainfield tornado and the 1967 Oak Lawn tornado serve as reminders of the potential for extreme danger in urban settings.
Recent studies suggest that tornado activity is shifting eastward from the Great Plains, placing Illinois and other Midwestern states in a zone of heightened risk. This migration reinforces the need for all communities in the state to maintain robust preparedness and warning systems.
Essential Tornado Safety and Preparedness
Understanding the difference between a Tornado Watch and a Tornado Warning is the first step in effective safety planning.
Tornado Watch
A Tornado Watch is issued when atmospheric conditions are favorable for tornado development in and near the watch area. This alert signals that residents should remain vigilant, monitor weather reports, and ensure their emergency supplies and safe locations are ready for use.
Tornado Warning
A Tornado Warning is a serious and immediate alert, meaning a tornado has been sighted visually or detected by weather radar. When a warning is issued for your location, immediate action is required to protect life and property. The National Weather Service advises moving to a safe place right away, as the danger is imminent.
Finding Shelter
The safest place during a tornado is an underground shelter, such as a basement or storm cellar. If no basement is available, the lowest floor of a sturdy building, in a small interior room like a closet, bathroom, or hallway, offers the best protection. It is important to stay away from windows, doors, and outside walls, as these are the first elements to fail during high winds.
Once in the safe location, cover your head and neck with your arms, a mattress, or a heavy blanket to guard against flying debris. Every household should have an emergency kit, including:
- A battery-powered NOAA Weather Radio.
- Water.
- Non-perishable food.
- A first-aid kit.