Above-normal temperatures in the West, Northwest and Southwest United States helped contribute to 2014 being the 18th consecutive year that temperatures exceeded the 20th century average.
The 2014 annual average contiguous U.S. temperature was 52.6 F, which is 0.5 F above the 20th century average, the National Climate Data Center (NCDC) reported. Overall, 2014 ranked as the 34th warmest year since 1895.
Arizona, California and Nevada all had their warmest year on record, according to NCDC.
The West was warmer than average for much of 2014, bringing the region to its warmest average temperature on record.
However, the Ohio Valley, including Indiana, Illinois, Kentucky, Missouri, Ohio and Tennessee, saw its ninth coolest year on record.
December closed out the year as the second warmest on record with an average U.S. temperature in the lower 48 states of 37.1 F, which is 4.5 F above the 20th century average.
December 2014 was the warmest since 1939, the data center said. Nine states across the West, southern Plains and Northeast had a top-10 warm December.