Tornado Review   5/2/2006


1. Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. These thunderstorms often produce large hail, strong winds, and tornadoes.

2. A funnel cloud is a similar column of air that is not in contact with the ground. A water spout is a tornado that is over water. When either a funnel cloud or a water spout comes in contact with the ground, it becomes, by definition, a tornado.

3. F0 and Fl tornadoes comprise 70% of all tornadoes that occur in the U.S. They usually touch down briefly and cause minor damage. However, forecasting these tornadoes is less reliable than for stronger tornadoes, so less than 50% occur during tornado watches.

4. F2 and F3 tornadoes comprise about 28% of the tornadoes in the U.S. They can cause significant damage, injuries, and deaths.

5. F4 and F5 tornadoes comprise about 2 percent of the tornadoes in the U.S. and cause 70% of the death and destruction. Fortunately, the NWS has identified precursor conditions for the more damaging tornadoes. Over 95% of these tornadoes, therefore, occur during tornado watches.

Tornadoes are associated with thunderstorms, so they may be preceded or followed by heavy rainfall or hail.  Source: FEMA Independent Study Program: IS-271 Anticipating Hazardous Weather & Community Risk




“While maybe not in the heart of tornado alley, Missouri and Illinois historically have ranked among the top 15 states in terms of tornado frequency, deaths and injuries.”

Tornado Warning Systems

Today's severe storm warning system consists of several steps on the national, local and private level. It all starts early in the morning at the National Severe Storms Forecast Center. Scientists and researchers look over the morning's weather maps, charts, satellite images and radar screens. As temperature readings and condition reports come in from throughout the country, the forecasters get a good idea of where conditions may be most favorable for the development of severe weather. The men and women keep a twenty-four hour shift at the center, and because they track only severe weather conditions, some call them "the keepers of the gates of hell" (Fuller 155). The meteorologists at the center, upon observing alarming conditions, will first issue a severe thunderstorm watch. This simply means that conditions are ripe for the development of severe thunderstorms. If conditions on the radar screens indicate that the storms are actually occurring, they will upgrade the watch to a severe thunderstorm warning. When these storms actually strike, the weather is usually also favorable for the development of tornadoes, so the forecasters will issue a tornado watch. The bulletin read with the watch will usually state: "TORNADO WATCH #--: BULLETIN- IMMEDIATE BROADCAST REQUESTED…TORNADOES..LARGE HAIL..DANGEROUS LIGHTNING POSSIBLE…PERSONS IN THE THREATENED AREAS SHOULD BE ON THE LOOKOUT (Fuller 157). After the tornado watch is issued by the center, the responsibility is passed on to the next level, which is the network of local weather stations across the country. When the weather stations receive this data, they will then broadcast it over all available media.

The last level of the countrywide warning system lies on the ground in the affected area. The bulletins first come out over National Oceanic and Atmospheric Association's weather radio. After this, fire and police departments, amateur radio operators, the media, and area Emergency Broadcast Systems spread the word. This then alerts the National Weather Service's Skywarn network. The network is made up of police officers, retirees, and any other person who feels concerned enough to be on the lookout for those who can't. When a tornado does from threatening skies, it is first spotted in one of two ways. If the local weather station has good radar equipment and the operator is experienced, a "hook echo" will appear on the monitor, and he will issue an immediate tornado warning. Hook echoes are fishhook patterns caused by rapidly rotating precipitation; this signals that the motion is present for a tornado to descend from the sky (Fuller 156). The other way is for someone to actually spot the tornado on the ground, but this is often too late to save its first victims.



􀂙 􀂙 Most tornado damage paths are less than 100 yards wide and a couple of miles long, but can

be up to a mile wide and 50 miles long.

􀂙 Most tornadoes occur in the spring, but records show that they have occurred in every

month of the year.

􀂙 In 2003, a record setting 120 tornadoes occurred in Illinois, resulting in two deaths, 81

injuries, and more than $40 million in damage. The previous record was 107

tornadoes, set in 1974.

􀂙 In 2004, 80 tornadoes occurred in Illinois, resulting in 9 deaths and 23 injuries.

􀂙 There were only 18 tornadoes in Illinois during 2005, with no deaths or injuries reported.

􀂙 There is an average of 38 tornadoes per year in Illinois.



Compared with other States, Illinois ranks number 7 for frequency of Tornadoes, 10 for number of deaths, 6 for injuries and 8 for cost of damages. When we compare these statistics to other States by the frequency per square mile, Illinois ranks, number 11 for the frequency of tornadoes, number 9 for fatalities, number 8 for injuries per area and number 7 for costs per area.


It's important to keep track of what is happening upstream (S.W.)  from our area. If we keep current on the meteorological conditions, we'll be better prepared for the destructive events. If we wait until the watches and warnings have been issued, we've waited too long.



Mokena Emergency Services & Disaster Agency

Tornado Facts for the area