There are a variety of severe weather hazards that affect Cook County, including lightning, damaging winds, large hail, flash floods and tornadoes.

Tornadoes pose the greatest severe weather threat to life and property in Cook County. Tornado season in Cook County is from mid March through June, but tornadoes have occurred in every month of the year. They are most frequently seen from mid afternoon through the early evening. Most tornadoes move from the southwest toward the northeast, but they sometimes move east or southeast. Tornadoes usually move at speeds of 30 to 40 mph, but they can move as fast as 70 mph. Most Cook County tornadoes produce wind gusts of 50 to 120 mph and last only a few minutes. Also, there are tornadoes that are large, violent and long- tracked with wind gusts of over 200 mph that can occur in Cook County.

Illinois averages 28 tornadoes per year. In 1999 there were 94 tornadoes in Illinois. This the second highest ever, behind 110 tornadoes in 1998. 46 tornadoes occurred in April 1996, and 45 of them occurred on one day – April 19. This was the largest number of tornadoes to ever touch down in Illinois in a day and the most ever for the month of April.

Tornadoes are not the only severe weather threat in Illinois. Nineteen people have been killed by lightning in the last 10 years and dozens more have been injured. Most lightning casualties occur in the summer between the hours of 10:00 a.m. to 7:00 p.m. Most victims are outdoors under a tree, in an open field, near a vehicle or near a building.

Floods and flash floods are the number one severe weather killer in the United States. Sixteen pepple have died in floods in Illinois in the last decade. Most flood casualties in Illinois occur in vehicles when people try to drive across flooded roads. Flash floods are most frequent in mid to late summer, but they can occur anytime.

Straight line or downburst winds from severe thunderstorms often reach speeds of 50 to 80 mph and sometimes exceed 100 mph. These winds down trees and large limbs, power lines and poles and cause severe structural damage to buildings. Significant damage can be seen in light weight buildings or weaker structures such as barns and out buildings. Mobile homes are also vulnerable to severe thunderstorm winds. Severe thunderstorms usually approach from the southwest or west, but can move from the northwest particularly in mid to late summer. Damaging winds often are preceded by a dark low-hanging row of clouds on the leading edge of an approaching storm, known as a shelf cloud.

Large hail can also accompany severe thunderstorms. Hail rarely causes injuries in Cook County but it can cause millions of dollars in damages to crops, vehicles, roofs of buildings and homes each year.

Cook County Sheriff Emergency Management Agency
1311 Maybrook Drive • Maywood, Illinois 60153
708.865.4766
Fax: 708.681.0504
ccsema@cookcountysheriff.org