The National Weather Service says this has been the most active tornado season since 1974. They say “La Nina” is to blame for the unusually high number of twisters across the Midwest and South this spring. Meteorologist Joe Sullivan says we were in “La Nina” all winter and that she contributed to a record 227 tornadoes across the South on April 27. La Nina is also blamed for the 13 (and counting) tornadoes that hit Indiana Wednesday. La Nina refers to cooler than normal sea surface temperatures off the coast of Peru. That system interacts with warmer air patterns that create more moisture and stronger storm activity. Sullivan says the La Nina pattern is finally weakening and that means we should be entering a drier weather pattern.