A tornado is a violently rotating column of air extending from a thunderstorm to the ground.
Illinois Average Tornado Count
Illinois experiences a number of tornadoes each year, averaging 54 based on data collected between 1991 and 2020. This 30-year average provides a meteorological standard for understanding the state’s typical tornado activity. While Illinois is not traditionally considered part of the main “Tornado Alley” in the Great Plains, its tornado frequency is comparable to states within that region. For instance, Illinois has been noted as having a high “Tornado Index” compared to other U.S. states.
Yearly Fluctuations and Trends
The annual number of tornadoes in Illinois can fluctuate significantly from the average. Some years have seen no tornadoes at all, such as 1919 and 1933, demonstrating the variability of these events. Conversely, other years have experienced high activity, far exceeding the average. For example, Illinois recorded 124 tornadoes in 2006, 121 in 2023, and a preliminary 142 in 2024, which would mark a new annual record.
These yearly differences are influenced by various atmospheric conditions, including the patterns of warm, moist air masses and the movement of cold fronts. Long-term trends in reported tornado numbers also reflect advancements in detection technology, such as the widespread use of Doppler radar, which allows for earlier and more accurate identification of rotating storms. Improvements in storm spotter networks and survey methods have also contributed to an observed upward trend in recorded tornado events over time. Additionally, observations suggest that tornadoes are occurring more frequently during months outside the traditional tornado season, potentially influenced by warmer and more humid winter conditions.
Seasonal and Geographic Patterns
Tornadoes in Illinois exhibit seasonal and geographic patterns. The primary tornado season typically spans from April through June, accounting for approximately 63% of the state’s tornado occurrences. During this period, the clash of warm, moist air from the Gulf of Mexico with cooler, drier air masses often creates unstable atmospheric conditions conducive to severe thunderstorms and tornado formation. A secondary peak in tornado activity can sometimes occur in the fall, and more tornadoes have been recorded in December and February combined than in September and October.
Geographically, tornadoes are common across central and northern Illinois, with these regions historically experiencing a higher density of events. Counties like Logan, Tazewell, and Sangamon in central Illinois frequently show higher normalized tornado rankings. While certain areas may experience more tornadoes, it is important to recognize that these powerful storms can strike anywhere within Illinois at any time of the year, underscoring the importance of preparedness across the entire state.