With better technology more tornadoes are detected and tracked enabling meteorologists to issue tornado watches and warnings to the most at-risk cities for costly damage.

Formation and Existence of Destructive Tornadoes

Tornadoes are the most violent meteorological event recorded, according to the National Oceanic and Atmospheric Administration (NOAA). The United States alone reports more than a thousand tornadoes each year. Climatologist predict that over double that amount, 2,000 tornadoes, actually happen across the United States per year, but remain unseen or unreported. The United States reports more tornadoes than any other country, due to the large land mass of the Great Plains, open to tornado develop. As cold air from the arctic collides with subtropical, warm air from the Gulf of Mexico, almost perfect conditions exist for tornado formation.

Home of "Tornado Alley"

Although tornadoes can form anywhere at anytime, there is one area of the United States that is plagued by tornadoes on an annual basis. The large span of open land between the Gulf of Mexico and the Rocky Mountains, is home to Tornado Alley. Tornado Alley is comprised of the area between central Texas, Oklahoma and Kansas, to as north as Nebraska and Iowa. Tornado Alley exists mostly in the spring and early summer months, from April to June. This is the time when the warm moist subtropical air moves upwards toward the cool, dry Arctic air from Canada.

When Tornadoes Hit

Though tornadoes can form at any time, the jet stream acts as an important part of tornado formation. Most tornadoes form in the afternoon, when the atmosphere is warmer, "creating unstable conditions at various altitudes" (Burt, 2004). Tornado formation usually occurs between the hours of 3pm and 9pm. Most tornadoes travel from southwest to northeast, along the movement of air fronts and thunderstorms.

Tornado Forecasting?

Tornadoes are extremely difficult if not impossible to forecast. Meteorologists can forecast conditions most likely to induce tornado formation but cannot predict when and where a tornado will happen. Forecasters can predict severe thunderstorms and the possibility for tornadoes but it's not a certain fact that a tornado will hit. Based on previous information, tornado statistics, and climatology data, meteorologists can issue watches and warnings for tornadoes. With increasingly advanced technology, storm chases are improving storm and tornado tracking. An increase in the number of reported tornadoes recently has been due to better technology in detection and tracking, such as Doppler Radar.

High Risk Cities For Occurrence of Tornadoes

Tornado expert climatologist, Thomas P. Grazulis, author of Significant Tornadoes: 1680 - 1991 has compiled data on the states and cities with the highest risk or occurrence of tornadoes. Using this data, cities can better prepare for tornadoes when they do hit. "Significant" tornadoes are based on the Fujita scale, meaning F2 or stronger, causing damage and destruction.

Enhanced Fujita Scale (EF Scale)

• F0 (Gale)
• F1 (Weak)
• F2 (Strong)
• F3 (Severe)
• F4 (Devastating)
• F5 (Incredible)

Most At-Risk Large U.S. Cities* (population 250,000 or more)

1. Oklahoma City, Oklahoma

2. Dallas - Fort Worth, Texas

3. Lubbock, Texas

4. Kansas City, Missouri

5. Indianapolis, Indiana

6. St. Louis, Missouri

7. Jackson, Mississippi and Birmingham, Alabama

8. Little Rock, Arkansas

9. Omaha, Nebraska

10. Chicago, Illinois

*Based on list in Extreme Weather

References:

Burt, Christopher C. Extreme Weather, a guide and record book. 2004. W.W. Norton & Co., NY.