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NOAA: U.S. December Wetter and Colder than Average

2009 yearly precipitation and temperature above average

January 12, 2010

NOAA’s State of the Climate report shows the December 2009 average temperature for the contiguous United States was 30.2 degrees F, which is 3.2 degrees F below average. Last month’s average precipitation was 2.88 inches, which is 0.65 inch above the 1901-2000 average.

For 2009, the contiguous United States averaged 53.1 degrees F, which was 0.3 degrees warmer than average. The U.S. averaged 31.47 inches of precipitation for the year, which was 2.33 inches above the long-term average. Based on data going back to 1895, the monthly analyses prepared by scientists at NOAA’s National Climatic Data Center, are part of the suite of climate services provided by NOAA.

U.S. Temperature Highlights

• The nationally-averaged temperature for December was below normal, as Arctic air dove deep into the United States. No region averaged above normal temperatures.
• Nebraska had its eighth coolest December, Texas, Nevada, and Wyoming their ninth, and Montana and Utah their tenth coolest. 
• 2009 yearly temperatures were above normal in parts of the South, Southwest and West, while much of the Central Plains and Midwest were below normal.

U.S. Precipitation Highlights

• The U.S. recorded its 11th wettest December on record, making 2009 the fourth consecutive December that the contiguous U.S. has seen above normal precipitation.
• It was the wettest December on record for Virginia, South Carolina, Georgia and Maryland. Thirteen states experienced December precipitation that ranked among their top ten wettest. Only Wyoming, Idaho, Oregon, and Washington had precipitation below the December long-term average.
• Several major cities, including Philadelphia, Washington, and Oklahoma City, had their snowiest Decembers on record.  

Other Highlights

• Several significant winter storms affected the United States in December. NOAA satellite observations showed the average snow extent for the contiguous U.S. was more than 4.1 million square kilometers - the largest for any December since the satellite record began in 1966.
  
• By the end of December, moderate-to-exceptional drought covered only 12.4 percent of the contiguous United States, based on the U.S. Drought Monitor. During the year, major drought episodes in California and South Texas improved significantly, while drought conditions emerged across much of Arizona, partly due to the weakness of this year’s North American monsoon season.
  
• About 43 percent of the contiguous United States had moderately-to-extremely wet conditions at the end of December, according to the Palmer Index.

NCDC’s preliminary reports, which assess the current state of the climate, are released soon after the end of each month. These analyses are based on preliminary data, which are subject to revision.  Additional quality control is applied to the data when late reports are received several weeks after the end of the month and as increased scientific methods improve NCDC’s processing algorithms.

Scientists, researchers and leaders in government and industry use NCDC’s monthly reports to help track trends and other changes in the world’s climate. The data have a wide range of practical uses, from helping farmers know what to plant, to guiding resource managers with critical decisions about water, energy and other vital assets.

NOAA understands and predicts changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and conserves and manages our coastal and marine resources.