Most tornadoes occur in the spring, but have occurred every month of the year. Most tornadoes produce winds 60 to 120 mph. The most violent tornadoes can produce winds up to 318 mph. There is an average of 29 tornadoes per year in Illinois. Illinois led all other states in 1998 in the number of tornadoes.
Thunderstorms can produce strong winds, lightning, hail or heavy rain.
Each year, more people are killed by lightning than by tornadoes. Twenty-one people have been killed by lightning since 1985 in Illinois. Thunderstorms are most likely to happen in the spring and summer. In Illinois, severe thunderstorms frequently occur in the late afternoon or evening. Large hail does extensive damage to property and crops every year.