Spring 2012: most extreme season in U.S. history
min/max sampling records are "difficult" to break (new records occur exponentially less frequently) only in a stationary distribution. When the distribution changes, all bets are off.
Spring 2012 in the contiguous U.S. demolished the old records for hottest spring and most extreme season of any kind, said NOAA's National Climatic Data Center (NCDC) on Thursday. With the warmest March, third warmest April, and second warmest May, the March - April - May spring season was 5.2°F above average--the largest temperature departure from average of any season on record for the contiguous United States. What's truly remarkable is the margin the old record was broken by--spring 2012 temperatures were a full 1°F above the previous most extreme season, the winter of 1999 - 2000.
All-time seasonal temperature records are very difficult to break, and are usually broken by only a tenth of a degree. To see the old record crushed by a full degree is a stunning and unparalleled event in U.S. meteorological history.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2115