Using tornado statistics provided by the National Climatic Data Center, here we explore the relationship of selected tornado characteristics with hour of the day, month of the year, from year to year, etc. This was part of a Capstone project by Michael Patrick, a senior (2011) in the Department of Atmospheric Science at the University of Illinois.
Figure 1. This plot shows the number of tornadoes per year from 1950 to 2010. The apparent upward trend over time is due to better tornado reporting since the mid 1990s thanks to better radar and spotter networks. This issue is discussed in more detail on the tornado trends page.
Figure 2. This plot shows the number of tornado-related fatalities from 1950 to 2010. The 1967 Belvidere and Oak Lawn event and the 1990 Plainfield event are the two standouts in the historical record.
Figure 3. This plot shows the number of tornado-related injuries from 1950 to 2010. On average, the number of injuries is 20 times higher than the fatalities from tornadoes.
Figure 4. This plot shows the number of tornadoes by month in Illinois. About 66 percent of all historical events occurred in April, May, and June. However, tornadoes can occur at any time in Illinois. Please take tornado watches and warnings seriously, regardless of the month.
Figure 5. This plot shows the number of tornado-related fatalities by month for Illinois. April is the deadliest month with 92 reported deaths. The second deadliest month was August, largely due to the 29 deaths associated with the August 28, 1990, Plainfield event.
Figure 6. This plot shows the number of tornado-related injuries by month for Illinois. April is the worst month for injuries. It is interesting that while April has a high frequency of tornadoes, deaths, and injuries, the number of deaths and injuries sharply in May and June even though the number of tornadoes is nearly as high as May and June. While I can only speculate, I think this is due in part to better preparation and response to tornado watches and warnings as the season progresses.
Figure 7. This plot shows the number of tornadoes by the time of day in Illinois. Tornadoes rarely occurred in Illinois between midnight and noon. However, the numbers rapidly increase each hour in the afternoon. They peak at 5 pm and decline through the rest of the evening.
Figure 8. This plot shows the number of tornado-related fatalities by hour in Illinois. Most of the fatalities occurred between 2 and 5 pm.
Figure 9. This plot shows the number of tornado-related injuries by hour in Illinois. Most of these occurred between 2 and 5 pm. It is interesting that the number of fatalities and injuries drop off sharply after 5 pm even though the number of tornadoes is relatively high from 5 to 9 pm. While I can only speculate (again), I think the sharp drop off after 5 pm is due in part to the fact that most people are home and settled with more access to weather warnings and better shelter.
Figure 10. This plot shows the number of tornadoes in each category of the Fujita scale. The good news about tornadoes in Illinois is that the majority are at the weaker end of the Fujita scale. In fact, the most type of event, an "EF0", tend to cause little if any damage and injuries or deaths are rare. The worst category of tornadoes, an "EF5", are extremely rare. Only three have occurred in the records since 1950.
Figure 11. This plot shows the number of fatalities in each category of the Fujita scale. As expected, the number of deaths increase as the tornado becomes more damaging. The lower number of total deaths in the EF5 category than the EF4 category are due to the very small number of EF5 events. If you recast the information as the average number of fatalities per event, the EF4 events yield 2.5 deaths per event while the EF5 events yield 10 deaths per event.
Figure 12. This plot shows the number of tornado-related injuries in each category of the Fujita scale. The pattern is similar to the number of fatalities.