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Washington • Spring in the contiguous U.S. was the warmest on record, capping the hottest 12-month period in data going back 117 years, the National Climatic Data Center said.
The national average temperature from March through May was 57.1 degrees Fahrenheit (14 Celsius), 5.2 degrees above the long-term average and 2 degrees warmer than the previous mark set in 1910, said the data center in Asheville, N.C.
The period from June 2011 through May was the warmest 12 months on record in the contiguous U.S. The national average temperature was 56 degrees, surpassing the old mark for May 2011 through April by 0.4 degree, the center said in its monthly "State of the Climate" report.
A record high national average temperature for January through May helped send natural gas to a 10-year low as less was needed to warm homes and businesses.
"The spring of 2012 was the culmination of the warmest March, third-warmest April, and second-warmest May," the report said. "This marks the first time that all three months during the spring season ranked among the 10 warmest since record-keeping began in 1895."
Forty-two states had top-10 warmest springs, with the period setting records in 31 states. Record-keeping began in 1895.
Meteorologists designate spring as being from March 1 through May 31. The calendar season starts spring on the equinox, which was March 20 this year, and ends it at the solstice, June 20.
For the year ended May 31, every state in the contiguous U.S. had above-average temperatures except Washington, which was near normal.
"The 12-month period encapsulated the second-warmest summer, fourth-warmest winter and the warmest spring on record," the center said.
The average May temperature in the lower 48 states was 64.3 degrees, the highest behind 1934, which was 65.4, according to the center.
As of May 29, 37.4 percent of the contiguous U.S. had drought conditions, down from 38.2 percent at the start of the month, the report said.
The U.S. also experienced a record number of extreme weather events, from temperatures to tropical storms, from March through May, according to the report. The U.S. Climate Extremes Index is at 44 percent, more than twice the mean of 20 percent.