Cameron L Crosby
Illinois is a state with fairly high tornado activity. While some areas in the Plains are in some years more active, Illinois's severe weather is significant in its own right. It is among the most active areas on the planet... The prime tornado season is March through June, although tornadoes do occur at any time of the year in Illinois. Most deadly tornadoes tend to occur in March-April-May, but also have occurred all throughout the year. Most tornadoes occur from mid-afternoon through early evening with the peak hour being 5 PM. Tornadoes can occur at any time however. Illinois has been struck by many large outbreaks, and does have a history of long-track, violent tornadoes. The larger tornadoes usually don't strike as frequently. Some of the worst severe weather and tornado episodes both meteorologically and socially have impacted Illinois. Most Illinois tornadoes are weak and short-lived. They most often move to the northeast, but often do not. Average forward speed is 30-40 MPH although they can be stationary or move over 70 MPH. They occasionally merge, "skip" (each distinct touchdown considered a separate tornado), exhibit multiple vortices, or change paths. They are not always visible or audible. Also, Illinois falls victim to something that rarely occurs in the southern Plains or Southeast, that is the derecho (widespread, violent convectively-induced windstorm). Illinois averages 30-50 tornadoes per year, the vast majority of these are weak. FEMA does describe the Illinois tornado threat as a "high risk" and much of the state lies within Wind Zone 4. A tornado shelter is recommended for all residences in Illinois. In addition to the tornado and straight-line wind threat, Illinois is also subjected to flash flooding, lightning, extreme heat and cold, blizzards, and ice storms. Thunderstorm winds produce much more damage than tornadoes due to their higher frequency and aerial coverage. While typically not as intense, they sometimes can approach the wind velocities of an F3 tornado. Keep your eyes to the skies...