When a hail storm moved through Fort Worth, Texas on May 5, 1995, it battered the highly populated area with hail up to 4 inches in diameter and struck a local outdoor festival known as the Fort Worth Mayfest.
The Mayfest storm was one of the costliest hailstorms in U.S history, causing more than $2 billion in damage and injuring at least 100 people.
Scientists know that storms with a rotating updraft on their southwestern sides -- which are particularly common in the spring on the U.S. southern plains -- are associated with the biggest, most severe tornadoes and also produce a lot of large hail. However, clear ideas on how they form and how to predict these events in advance have proven elusive.