What was the biggest outbreak of tornadoes?
147 tornadoes touched down in 13 U.S. states on 3 and 4 April, 1974. Here is a map of them , with F-scale damage plotted beside each. [One more tornado touched down in Canada at Windsor ON, then lifted as it entered MI, for a total of 148. Since it did no damage in the U.S., it is not counted in the U.S. tornado database used to plot our map.] The outbreak killed 310 in the U.S., 8 in Canada, with 5454 U.S. injuries and 23 hurt in Canada. 48 of the tornadoes were killers. Seven produced damage rated F5 — the maximum possible — and 23 more were rated F4. This was one of only two outbreaks with over 100 confirmed tornadoes, the other being with Hurricane Beulah in 1967 (115 tornadoes). In 1999, NOAA Public Affairs created a large website on the 1974 super-outbreak in commemoration of its 25th anniversary. SPC also has a list of web links devoted to this and other major tornado events.
