Tornado Season in Illinois

Across 1996 to 2025, the middle 80 percent of Illinois's tornado days fell between Mar 30 and Sep 9, and the busiest month was May with 25.7 percent of the tornado days. The busiest single week is centred on May 28. The months carrying at least a twelfth of the year's tornado days are April, May, June, July. Those are percentiles of what happened, not a boundary: one tornado day in ten fell before that opening date and one in ten after the closing date.

Illinois recorded 1934 tornadoes over the 30 years from 1996 to 2025, which works out at 65 a year, spread over 17 tornado days a year. 210 were rated EF2 or stronger, the bar the Storm Prediction Center calls a significant tornado, and 7 reached EF4 or EF5. Another 129 carry no rating at all (7 percent of the total), so every intensity figure here covers rated tornadoes only. These are counts of tornadoes, not of database rows: the SPC file stores long tracks as several segments and this site counts each tornado once per state it touched.

The strongest Illinois tornado in this window was rated EF4, beginning in Tazewell County on 2013-11-17, with a path 46.36 miles long. The National Weather Service pairs a EF4 rating with estimated 3 second gusts of 166-200 mph. A rating is a damage survey verdict, not a measurement: in the NWS's own words, "The EF scale still is a set of wind estimates (not measurements) based on damage." The agency's records attribute 53 deaths to Illinois tornadoes across the whole 30 year window.

about 1 in 10 of Illinois's tornadoes in this window touched down between 9 pm and 6 am local standard time (12 percent), and the single busiest hour of its day is the one beginning at 5 pm. The night share is worth knowing because it varies enormously by region: near zero on the high plains, where storms live and die with afternoon heating, and around three in ten in the Gulf South, where tornadoes ride overnight squall lines. These hours come from converting the database's Central Standard timestamps to each tornado's approximate local standard time using its longitude.

Counting each tornado once per county it touched, the top of the Illinois list for 1996 to 2025 is Will County with 56, Logan County with 53, Sangamon County with 53. Read county counts with SPC's own caveat in mind: the database is built from reports and surveys, so counties with more people and more roads verify more tornadoes than empty ones with the same weather. The full table, and a ZIP code lookup that reads it, is on this page.

The National Weather Service's own definitions, in short: a watch means be prepared, a warning means take action. Verbatim: "Tornado Watch: Be Prepared! Tornadoes are possible in and near the watch area. Review and discuss your emergency plans, take inventory of your supplies and check your safe room. Be ready to act quickly if a warning is issued or you suspect a tornado is approaching. Acting early helps to save lives! Watches are issued by the Storm Prediction Center for counties where tornadoes may occur. The watch area is typically large, covering numerous counties or even states." And: "Tornado Warning: Take Action! A tornado has been sighted or indicated by weather radar. There is imminent danger to life and property. Move to an interior room on the lowest floor of a sturdy building. Avoid windows. If in a mobile home, a vehicle, or outdoors, move to the closest substantial shelter and protect yourself from flying debris." This page reads both live from api.weather.gov and shows them exactly as issued.

The record cannot answer that. The Storm Prediction Center is blunt about its own database: "Tornado reports have increased, especially around the installation of the NEXRAD Doppler radar system in the mid 1990s. This doesn't mean that actual tornado occurrence has gone up, however." The growth is almost entirely in weak tornadoes that better radar, more chasers and more cameras now document. That is why this site computes everything inside the Doppler era (1996 to 2025) and leads with tornado days rather than raw counts.

The NOAA Storm Prediction Center Severe Weather Database, the National Weather Service's own record of every United States tornado since 1950, which is a US Government work in the public domain. These pages use the 1996 to 2025 window and count tornadoes rather than database rows: the file stores each long track as several segments, and the counting rule is verified against SPC's own de-segmented file at build time. County names come from the US Census Bureau. Live warnings come from api.weather.gov and are shown verbatim.