Tornado Plots for Illinois
Using tornado statistics provided by the National Centers for Environmental Information here we explore the relationship of selected tornado characteristics with hour of the day, month of the year, from year to year, etc. This was part of a Capstone project by Michael Patrick, a senior (2011) in the Department of Atmospheric Science at the University of Illinois. All the plots have been updated through 2025. Click any plot to enlarge.
Tornadoes and Fatalities by Year
The apparent upward trend over time is due largely to better tornado reporting since the mid 1990s because of improved radar and spotter networks. This issue is discussed in more detail on the tornado trends page. It’s worth noting that each of the the past three years – 2023, 2024, 2025 – have been among the top 5 most active statewide.
The 1967 Belvidere and Oak Lawn events and the 1990 Plainfield event are the two tornado fatality standouts in the historical record.
Tornadoes and Fatalities Month
About 60 percent of all historical events occurred in April, May, and June. However, tornadoes can occur at any time in Illinois.
April is the deadliest month with 97 reported deaths. The second deadliest month was August, mostly due to the 29deaths associated with the August 28, 1990, Plainfield event.
Importantly, December and February are among the deadliest months for tornadoes, historically. In fact, between 1950 and 2025, there was one fatality for every 4.5 December tornadoes in Illinois and every 6 February tornadoes. Comparatively, there was one fatality for every 29 May tornadoes, 59 June tornadoes, and 154 July tornadoes in Illinois.
Tornadoes and Fatalities by Hour of the Day
Tornadoes rarely occurred in Illinois between midnight and noon. However, the numbers rapidly increase each hour in the afternoon. They peak at 5 pm and decline through the rest of the evening. Nearly 60% of all tornadoes between 1950 and 2025 in Illinois occurred between 3 and 8 pm.
Most of the fatalities occurred between 2 and 5 pm, and rapidly decline after 5 pm. Between 1950 and 2025 in Illinois, there was one fatality for every 9 tornadoes that occurred between 2 pm and 5 pm, and one fatality every 33 tornadoes that occurred between 6 pm and 9 pm.
Tornadoes and Fatalities by F-Scale
We use the Enhanced-Fujita (EF) scale to rate tornado intensity, which is based on post-event assessment of damage. The good news about tornadoes in Illinois is that the majority are at the weaker end of the EF scale. In fact, the most frequent tornadoes are EF0 intensity, which tend to cause little if any damage and injuries. The worst category of tornadoes, an “EF5”, are extremely rare. Only three have occurred in the records since 1950.
Both total fatalities and fatalities per tornado increase with tornado intensity. The 3 EF-5 tornadoes that occurred in Illinois between 1950 and 2025 have an average rate of 10 deaths per event, compared to fewer than 1 death per event for EF-3 and weaker tornadoes.
However, because EF-3 tornadoes occur much more frequently than EF-5s, the former are responsible for 30 more deaths than the latter since 1950.
Tornado Trends
Tornado Trends in Illinois
Here is an example of how the method for collecting data changes over time, causing a signal that looks like climate change. The first figure shows the annual number of tornadoes per year in Illinois since 1950, regardless of strength. Beginning in the 1990s, the number of tornadoes has increased dramatically with wider variations from year to year.
The second figure shows the upward trend in the number of the weakest F0 (EF0) tornadoes. These rarely cause any damage and traditionally were ignored. The upward trend in recent years is the result of better radar systems, better spotter networks, and increased awareness and interest by the public. Combined these factors have allowed for a better documentation of the weaker events over time.
The third figure shows a much weaker trend in the stronger tornado events – those classified as F1 to F5 in the original Fujita Scale, and EF1 to EF5 in the Enhanced Fujita Scale. These represent the tornadoes that cause at least moderate damage, are well documented, and perhaps less sensitive to data collection methods.
