Unlike hurricanes, tornadoes give little warning and strike suddenly. Here are the top 15 deadliest tornadoes in United States history as of 2010.
(Note: these are the deadliest U.S. tornadoes, not the deadliest individual tornado days.)
March 18, 1925 Tri-State (MO/IL/IN) 695 deaths
May 6, 1840 Natchez MS 317 deaths
May 27, 1896 St. Louis MO 255 deaths
April 5, 1936 Tupelo MS 216 deaths
April 6, 1936 Gainesville GA 203 deaths
April 9, 1947 Woodward OK 181 deaths
April 24, 1908 Amite LA, Purvis MS 143 deaths
June 12, 1899 New Richmond WI 117 deaths
June 8, 1953 Flint MI 115 deaths
May 11, 1953 Waco TX 114 deaths
May 18, 1902 Goliad TX 114 deaths
Mar 23, 1913 Omaha NE 103 deaths
May 26, 1917 Mattoon IL 101 deaths
June 23, 1944 Shinnston WV 100 deaths
- April 18, 1880 Marshfield MO 99 deaths
Interestingly, tornadoes seem to be largely a U.S. phenomenon. Tornadoes occur in nearly all parts of Europe, but they are far less common and appear in less violent forms than in the U.S.
Statistics show that most tornadoes in the U.S. occur between 5PM and 6PM. However, those times vary by region; for example, Florida tornadoes are just as likely to occur after midnight as in the afternoon.
Where Tornadoes Form
Tornadoes frequently form in an area called, "Tornado Alley." Why? Located in the Great Plains, this area frequently receives warm, moist air from the Gulf of Mexico. Under certain circumstances, this air can fuel the formation of tornadoes.
For example, heat and moisture can build up near Earth's surface if a stable air layer called a cap lies on top. If the cap weakens, the lower, unstable air rises rapidly, often forming super-cell thunderstorms that spawn tornadoes.
Where Tornadoes Don't Form
Tornadoes do not touch down that often in big cities. Tornadoes require three factors to grow: vertical movement, which generally comes from thunderstorms; a significant variation in both wind speed and direction within the thunderstorm or air mass; and plenty of space for the rotation to develop.
That need for wide open spaces is why you hear about tornadoes so much in the plain states and flat areas of the Midwest and West. Tornadoes are unusual in cities because they lack the open space to develop.
Still, it's not entirely impossible. On May 12, 1997, a tornado struck very near downtown Miami, Florida, and lasted about 15 minutes. Some people were injured and it caused $525,000 in damages. That tornado developed over open water, which provided the space for it to grow, and then moved onshore.
When you look at it in terms of dollars of damage, that honor goes to Texas, where tornadoes cause an average of $43 million in damage each year. Second place goes to Indiana, and Kansas ranks third.
For what it's worth, the states of West Virginia, New Hampshire, Maine, Delaware, Hawaii, Idaho, Vermont, Washington, Rhode Island, Nevada, Utah, and Alaska don't even make the charts in terms of annual damage from tornadoes.
Remember: Tornadoes can form at any hour, so if your area is prone to these storms, have an emergency plan in place. See the related article above on "How to Survive a Tornado."