2006: hottest year in U.S. history.

Preliminary analysis of weather data gathered from more than 1,200 sites across the continental United States indicates that last year was the warmest on record.

The average temperature for 2006 was 12.8[degrees]C (55[degrees]F), National Oceanic and Atmospheric Administration (NOAA) scientists reported on the agency's website Jan. 9. That's about 1.2[degrees]C above the average temperature for the 20th century and 0.04[degrees]C warmer than the previous yearly record, set in 1998, says Richard Helm, a meteorologist at NOAA's National Climatic Data Center in Asheville, N.C.

That year began during the strongest El Nino ever recorded (SN: 12/11/99, p. 374). Changes in weather patterns during E1 Ninos typically warm winter temperatures across much of North America.

The latest El Nino began around the end of September, says Helm. Despite a frigid start to December in many areas, five states had their warmest Decembers ever, and no state measured below-average temperatures for that month. "Mother Nature fooled all of us and gave us a warm spell," he notes.

With temperatures above average from October through December, the nation's home-energy consumption was about 13.5 percent lower than it would have been if temperatures had been normal, the NOAA scientists estimate.