The map above shows anomalies compared to the average from 1981-2010, which in itself is a shifted baseline since temperatures started to warm up noticeably in 1986.
Over 16,000 high-temperature records were broken in the U.S. during March 2012, and by large margins of around 4.5° Centigrade or 9.8° Fahrenheit. The U.S. Northeast was particularly warm, which enabled tornadoes to form. The Pacific Northwest coast was cooler than usual right along the ocean. All regions except the Pacific Northwest had unusual temperatures, with either above-average temperatures or an unusual number of warm days: “NOAA confirms unprecedented warmth in March.” Maps are available at NOAA.
The map below shows state temperature records for March. The red is warmest in 118 years. The orange is warmest in 113 – 117 years, and so on.