April's Tornadic, Dangerous Reputation
While tornadoes can be spawned any time of year the volatile mix of climatological ingredients exist, April is a particularly dangerous month for tornadoes in parts of the U.S.
In the period between 1991-2015, April comes in only behind May and June for average U.S. tornado counts. That average is admittedly skewed by April 2011, in which 758 U.S. tornadoes set a record for any month.
A swath from the central and southern Plains east into the Tennessee Valley is most susceptible to swarms of tornadoes in the first full month of spring. However, the tornado threat also rises markedly in April much farther north into the Mississippi and Lower Ohio Valleys.
Dating to 1950, here is a list of metro areas who have seen a peak in tornadoes during the month of April, according to severe weather expert Dr. Greg Forbes:
Birmingham, Huntsville and Tuscaloosa, Ala.
In addition, while not necessarily a peak month, many more metro areas have experienced a significant rise in tornado counts in April, compared to March:
[T]he three worst tornado outbreaks in U.S. history, according to Forbes, all occurred in April:
April 3-4, 1974 "Superoutbreak"
April 26-28, 2011 "Superoutbreak"
April 11-12, 1965 "Palm Sunday Outbreak"