Friday, January 8, 2010

December 2009 14th Coldest, 11th Wettest in U.S.
Maryland, Virginia Had Wettest December

The National Climatic Data Center (NCDC) preliminary analysis for December 2009, posted earlier this afternoon, shows that the third warmest November was followed by the 14th coldest December in the contiguous U.S. The monthly average temperature of 30.2° F was 3.2° F below the long-term average. None of the 9 climate regions had above-average temperatures. Six states had top-ten coldest Decembers:
  • 8th coldest: Nebraska
  • 9th coldest: Texas, Nevada, and Wyoming
  • 10th coldest: Montana and Utah
For the entire year 2009, temperatures averaged 53.1° F, which was 0.3° warmer than the long-term average. This ranks the year as the 35th warmest in records dating back to 1895.

In contrast to temperatures which were below average, precipitation was above average for the month. The national average of 2.88", 0.65" above the 20th Century average, placed the month as the 11th wettest December. The Southeast region had its wettest December ever, including 3 individual states with wettest Decembers. A total of 13 states had top-ten wettest Decembers:
  • Wettest: Maryland, Virginia, South Carolina, Georgia
  • 2nd wettest: New Jersey
  • 3rd wettest: North Carolina, Alabama, South Dakota
  • 4th wettest: Iowa
  • 5th wettest: Delaware, Louisiana
  • 7th wettest: Minnesota, Florida
Only 4 states had lower than average precipitation: Wyoming, Idaho, Oregon, and Washington.

As would be expected for a cold winter month with heavy precipitation, snowfall was widespread during December. The Rutgers Global Snow Lab reported that the satellite-derived average snow cover extent of 4.1 million square km was the largest since satellite observations began in 1966. At the end of the month, slightly over 60% of the area of the contiguous 48 states was covered with snow.

Several major cities, mainly in the Mid Atlantic and Midwest, set records for December snow totals:
December 2009 Monthly Snow Records
City December 2009 Previous Record
Philadelphia, PA 24.1 inches 22.4 inches - 1909
Topeka, KS 19.2 inches 18.8 inches - 1983
Lincoln, NE 24.3 inches 22.3 inches - 1945
Omaha, NE 24.9 inches 19.9 inches - 1969
Oklahoma City, OK 14.0 inches 9.0 inches - 1914
Beckley, WV 37.8 inches 26.5 inches - 1993
Washington, D.C. 16.6 inches 16.2 inches - 1962
Balitmore, MD 23.2 inches 20.4 inches - 1966
Sioux City, IA 34.0 inches 22.6 inches - 2008
Jackson, KY 17.6 inches 11.5 inches - 1993
Des Moines, IA 28.2 inches 26.9 inches - 2000
Images (click to enlarge): U.S. December average temperature since 1895, statewide temperature and precipitation ranks for December 2009, daily U.S. percentage snow cover, December 31 snow cover; all from National Climatic Data Center/NOAA

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