Why April is a dangerous month for tornadoes.

 Over the past ten years there have been 758 tornadoes in the month of April more than any other month. Dating since 1950 the Metro cities of Atlanta, Birmingham, Cincinnati, Dallas, Little Rock, and Memphis have seen the most Tornado activity. And Cities such as Chicago, Houston, Kansas City, Lubbock, Nashville, St. Louis, and Wichita have seen a large increase in Tornado activity from the month of March to April. The three worst tornado outbreaks in history have occurred in April, April 3-4, 1974 nicknamed the "Superoutbreak", April 26-28, 2011 also nicknamed "Superoutbreak", and the third worst tornado outbreak in history occurred April 11-12, 1965 "Palm Sunday Outbreak".

Average April Jet stream. 

U.S. map of average Tornado Risk