U.S. smashes heat record for season Amanda Diaz, bottom left, reads a book as Ciara Perez, top left, and Chris Elam sit in a tree during the unseasonably warm weather in the Rittenhouse Square park Tuesday, March 13, 2012, in Philadelphia. AP Photo/Alex Brandon (AP) WASHINGTON - Call it spring's fever. Federal records show the U.S. just finished its hottest spring on record. March, April and May in the Lower 48 states beat the oldest spring temperature record by a full 2 degrees. The three months averaged 57.1 degrees, more than 5 degrees above average. That's the most above normal for any U.S. season on record. Meteorologists define those three months as spring. Warmest winter in a decade impacting economy The National Oceanic and Atmospheric Administration also reported Thursday that it was the second warmest May since records began in 1895. May averaged 64.3 degrees, just behind 1934. The first five months of 2012 were the hottest start to a year in U.S. weather record history. The 12-month period starting last June is also the hottest on record. Meteorologists blamed a persistent weather pattern.