Tornado climatology
The United States averaged 1,274 tornadoes per year in the last decade. April 2011 saw the most tornadoes ever recorded for any month in the US National Weather Service's history, 875; the previous record was 542 in one month. It has more tornadoes yearly than any other country and reports more violent (F4 and F5) tornadoes than anywhere else.
Tornadoes in the United States
The United States has seen 58 F5 and EF5 (the highest intensity and damage ranking) tornadoes since records began in 1950. No tornadoes prior to 1950 were officially ranked F5, due to inadequate engineering data and other information on the historical tornadoes. From 1950–1970 tornadoes were assessed retrogressively, primarily using information recorded in government databases, and newspaper photographs and descriptions. Beginning in 1971, tornadoes were rated by the NWS using on-site damage surveys.