Fast Facts about Tornadoes

Some Significant Tornadoes

Deadliest -- The Tri-State Tornado Outbreak of March 18, 1925 killed 689 people in Missouri, Illinois and Indiana. Murphrysboro, Ill., had 234 of those deaths, and West Frankfort, Ill., had 127.

Other deadly tornadoes include the May 6, 1840 tornado which killed 317 people in Natchez, Mississippi; the May 27, 1896, tornado which killed 255 in St. Louis, Missouri. Tornadoes on successive days in 1936 killed 216 people in Tupelo, Mississippi, on April 5; and 203 people in Gainesville, Georgia, on April 6.

Biggest, Costliest Outbreaks -- The April 3-4, 1974 Super Outbreak was the largest known outbreak, with 148 tornadoes in 11 states, killing 315 people, injuring more than 5,300 and causing $600 million in damages. Alabama, Kentucky and Ohio were the states hardest hit. Perhaps the most notable tornado of the outbreak was one which touched down southwest of Xenia, Ohio. The violent tornado destroyed half the town, killing 34 and causing property damages of more than $100 million.

The second most devastating outbreak of tornadoes of modern record was the 1965 Palm Sunday outbreak. Severe thunderstorms in the Upper Midwest spawned a total of 51 tornadoes within twelve hours. Indiana, Ohio and Michigan were hardest hit. The tornadoes killed 256 people and caused more than $200 million in damages. Two powerful tornadoes, about 30 minutes apart in time, traveled nearly identical paths across Branch, Hilsdale, Lenawee and Monroe counties in extreme south central and southeastern Lower Michigan. The tornadoes killed 44, and caused more than $32 million in damages to those areas. In Lenawee County, the damage path was up to four miles in width.

For lists of other deadly and destructive U.S. tornadoes, refer to the following Internet site: http://www.spc.noaa.gov/climo/

Tornado Season

Tornadoes can occur at any time of the year. In the southern states, peak tornado occurrence is in March through May, while peak months in the northern states are during the summer. Tornadoes are most likely to occur between 3 and 9 p.m. but have been known to occur at all hours of the day or night.

Watches versus Warnings

Many people confuse the meaning of a tornado "watch" and tornado "warning" issued by the National Weather Service. Here's the difference:

Watch: Tornadoes are possible in your area; remain alert for approaching storms.

Warning: A tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your pre-designated place of safety.

Fujita Tornado Intensity Scale

Category F0: Gale tornado (40-72 mph); light damage. Some damage to chimneys; break branches off trees; push over shallow-rooted trees; damage to sign boards.

Category F1: Moderate tornado (73-112 mph); moderate damage. The lower limit is the beginning of hurricane wind speed; peel surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads.

Category F2: Significant tornado (113-157 mph); considerable damage. roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light-object missiles generated.

Category F3: Severe tornado (158-206 mph); Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.

Category F4: Devastating tornado (207-260 mph); Devastating damage. Well-constructed houses leveled; structure with weak foundation blown off some distance; cars thrown and large missiles generated.

Category F5: Incredible tornado (261-318 mph); Incredible damage. Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile sized missiles fly through the air in excess of 100 yards; trees debarked; incredible phenomena will occur.

Safety and Preparedness

It is important to remain alert to signs of an approaching tornado and seek shelter if threatening conditions exist. Look for environmental clues including a dark sky, large hail or a loud roar.

If a warning is issued, move to a pre-designated shelter such as a basement; stay away from windows; get out of automobiles and lie flat in a ditch or depression; do not try to outrun a tornado in your car.

Internet Sources

More information on tornadoes and severe weather is available on the Internet at:

http://www.srh.noaa.gov/oun/
http://www.spc.noaa.gov/
http://www.nws.noaa.gov/om/brochures/tornado.htm
http://www.nssl.noaa.gov/noaastory/book.html