Are you prepared for Chicago's severe weather season?

Illinois had more tornadoes last year than any other state. In 2023, 120 tornadoes were reported, nearly tripling the number reported in 2022. Last year tied 2003 for the second-most tornadoes in our state since records began over 70 years ago. The only year that saw more tornadoes was 2006 when 124 tornadoes were reported. 

Meteorological spring starts on Friday, and March is when the severe weather season starts to ramp up. There is a risk of severe storms on Tuesday. More on that below.

Campton Hills twin tornadoes from July 12, 2023. (Courtesy Bob Waszak)

To qualify as a report of severe weather, a thunderstorm has to produce either a tornado, 1" diameter hail or larger, or winds equal to or exceeding 58 mph. Illinois has already had two tornadoes reported this year, along with four reports of damaging winds and 10 reports of large hail.

The number of days with at least one or more severe thunderstorm reports peaks in July for Illinois. Historically, the period of May, June, and July collectively have more severe storm reports than any other three-month period. In descending number of severe thunderstorm reports, after those months, it's August, September, April, March, November, February, December, and January.

In terms of tornado reports, May usually has the most, followed by June, August, July, April, September, and March. The graphic above shows the average number of days with at least one or more tornado reports per month. 

The Storm Prediction Center has five risk categories when it comes to severe thunderstorms. Understanding the spectrum of risk is helpful as we enter into a severe weather season. The categories from lowest to highest risk are marginal, slight, enhanced, moderate, and high.

On the low end, a marginal risk means isolated severe thunderstorms are possible. They should be "limited in duration and/or coverage and/or intensity."

At the other end of the spectrum, a high risk means widespread severe thunderstorms are likely. They should be "long-lived, very widespread and particularly intense."

The Chicago area is in a slight risk for severe thunderstorms late Tuesday afternoon into Tuesday night. A slight risk means scattered severe storms are possible. They should be "short-lived and/or not widespread." However, "isolated intense storms are possible."

Here are some helpful websites to get prepared for possible severe weather this year:

The most important thing to do is be weather aware. Make sure you have multiple ways of receiving severe weather alerts.