In yesterday’s post, I showed a plot of the number of tornado events in Illinois by month. I redid the figure today to express the monthly distribution as a percentage of the total. We had 2239 events covering the period from 1950 to 2010, considering tornadoes in all EF categories. Here is the breakdown by month showing the highest percentages in April-June, and November with 3 percent of the total.
There is a slightly higher risk of tornadoes in November than in October or December, but it’s just one percentage point higher. And there is another similar bump in August. The takeaway point is that there is a tornado risk in Illinois for every month of the year. You can find more tornado graphs on our ISWS tornado climatology page.
Tornado tracks for previous tornadoes in November (1950-2010). You can see more maps on our ISWS tornado tracks page.