“Contrasting air masses of widely-varying temperatures is the key. Active tornado seasons in the U.S. are always the result of UNUSUALLY COLD air pushing much farther south than normal through the Midwest into Dixie.”

He goes on to add: “For example, the ‘poster child’ for active tornado seasons was the so-called ‘Super Outbreak’ in April of 1974, which took place during a period of widespread global cooling. (Some thought that we were entering a new ‘Little Ice Age.’)”

During this ‘La Nina’ spring, we’ve seen a much cooler and wetter than normal period that has significantly delayed the planting of corn east of the Mississippi River in the Midwest. There is no doubt that these La Nina years favor far more tornadoes than usual.

http://www.cdapress.com/