Chapter Hazard Analysis

Map 2-4. Chicago Area Tornadoes



Source: Prof. Ted Fujita, University of Chicago






Source: Chicago Tribune, August 28,1990



F
Map 2-5. Tornado Frequency



Source: Illinois Emergency Management Agency
requency: Approximately 1,000 tornadoes occur each year in the United States. Illinois is tied for 7^th in the United States with an average of 26 tornadoes per year. Tornadoes are most likely to occur in April through June, but a tornado can occur at any time. Over half hit between 3:00 and 7:00 p.m. There are no official recurrence intervals calculated for tornadoes.

Kane County has had 15 of the 1,472 tornadoes recorded in Illinois between 1950 and 1999. Kane County is classified as having a high tornado risk based on historic tornado wind speeds and the number of recorded tornadoes per 1,000 square miles.

With 15 occurrences over 50 years, the likelihood of a tornado hitting somewhere in the county is 0.3 (30%) in any given year. Assuming a tornado affects one square mile and there are 524 square miles in Kane County, the odds of a tornado hitting any particular square mile in the County is 1 in 1,750 each year or a 0.0006% chance.

Safety: Although recent tornadoes in Kane County did not kill anyone, tornadoes are still killers. The August 1990 twister caused 28 deaths. The table below shows the tornado related fatalities in the United States for the last five years and where they occurred. The number of people who live in mobile homes is far smaller than the number who live in permanent homes, however they have practically the same number of deaths.

The table shows that the residents in mobile homes are at the greatest risk. There are seven mobile home parks within Kane County.