Category EF4 Wind in mph: between 166- 200. Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
Category EF5 Wind in mph: 200+. Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yards); trees debarked; incredible phenomena will occur.
March 18, 1925 - One of the worst tornado disasters in the United States; 695 people in the tri-state area of Missouri-Illinois-Indiana are killed. It is the longest-lived and has the longest path of any recorded U.S. tornado.
1950 - The U.S. begins keeping official records about tornadoes.
April 3-10, 1974 - There are 148 tornadoes in 16 states.
May 12-18, 1995 - There are 173 tornadoes in 18 states.
May 5-10, 2003 - There are 395 tornadoes reported in 19 states.
Feb. 2, 2007 - At least 20 people are killed in Lake and Volusia counties in Florida after at least three tornadoes touch down in the middle of the night.
March 1, 2007 - At least 20 people are killed, one in Missouri, 10 in Alabama, and nine in Georgia from a string of tornadoes. In Alabama, eight of the 10 killed are teenagers from Enterprise High School in Enterprise, Ala.
February 5, 2008 - At least 56 people are killed, 32 in Tennessee, 13 in Arkansas, seven in Kentucky, and four in Alabama from a string of tornadoes.
March 14, 2008 - A tornado reaching EF-2 strength at times hits downtown Atlanta, damaging the World Congress Center, CNN Center, the Georgia Dome, Cotton Mill Lofts, and many other buildings.
May 9-11, 2008 - A series of tornadoes kills 22 in three states including six in Ottawa County, Okla.; 13 in Newton County, Mo.; one in Jasper County, Mo.; one in an area of Purdy in Barry County, Mo., and one in Laurens County, Ga.
April 14-16, 2011 - At least 114 tornadoes touch down in Oklahoma, Kansas, Louisiana, Mississippi, Alabama, Missouri, Illinois, Georgia, South Carolina, North Carolina, Virginia, Maryland, Arkansas and Pennsylvania. Of the 46 fatalities reported, 23 occur in North Carolina.
April 25-28, 2011 - An outbreak of 201 confirmed tornadoes occurs from 8 a.m. ET April 25 to 8 a.m. ET April 28, 2011. There are approximately 321 fatalities in six states during the entire outbreak from April 25 to April 28. The majority of fatalities occur in Alabama, where as many as 243 people perish. Other states reporting fatalities are Mississippi, Tennessee, Georgia, Virginia and Arkansas. In terms of multi-day outbreaks, this outbreak holds the record for the largest number of tornadoes.
May 22, 2011 - An E5 tornado strikes Joplin, Mo., killing at least 158 people. It is the deadliest single U.S. tornado since federal record-keeping began in 1950. The tri-state tornado of 1925 is still the deadliest tornado in U.S. history.
May 24, 2011 - Tornadoes strike Arkansas, Oklahoma and Kansas, killing at least 18 people.
August 3, 2011 - The Storm Prediction Center's final report for April 2011 shows 753 tornadoes touched down across the U.S., breaking the previous monthly record of 543 tornadoes in May 2003.
March 2-3, 2012 - At least 42 tornadoes sweep across 10 states, killing 39 people. Of the 39 fatalities reported, 21 occur in Kentucky, 13 in Indiana, three in Ohio, one in Alabama and one in Georgia.
Top 10 deadliest single U.S. tornadoes:
March 18, 1925 - Tri-state area of Missouri, Illinois and Indiana - 695 fatalities.
May 6, 1840 - Natchez, Miss. - 317 fatalities.
May 27, 1896 - St. Louis, Mo. - 255 fatalities.
April 5, 1936 - Tupelo, Miss. - 216 fatalities.
April 6, 1936 - Gainesville, Ga. - 203 fatalities.