December 2005 started with unusually cold conditions across much of the nation but ended with record heat and wildfires in the southern Plains and strong storms in the Far West. The nationally averaged temperature for the month of December was near the long-term average, according to the NOAA National Climatic Data Center in Asheville, N.C. The Pacific Northwest and areas east of the Mississippi experienced colder-than-average temperatures, and the Southwest and northern Plains had warmer-than-average conditions. NCDC also reported precipitation was at-or-near record low levels in the southern Plains and Southwest, while areas from central California to the Pacific Northwest were much wetter than average. The global average temperature for December was ninth warmest on record.

NCDC scientists said the average temperature for the contiguous United States for December (based on preliminary data) was 33.5 degrees F degrees (0.8 degrees C), identical to the 1895-2004 mean. Colder-than-average conditions covered much of the nation during the first half of the month, as upper-level winds steered Arctic air into the southern U.S. A strong snowstorm moved across the Midwest and Northeast Dec. 8 and 9, and a damaging ice storm struck parts of the Southeast mid-month. (Click NOAA image for larger view of December 2005 state temperature rankings. Please credit “NOAA.”)

Atmospheric circulation changes during the last two weeks of the month brought a retreat of the Arctic air mass and put the country under the influence of warmer air from the Pacific. Temperatures for the last week of December were more than 15 degrees F above average in areas of the northern Plains and West, which had experienced extremely cold conditions in early December. For the year as a whole, the contiguous U.S. was 1.2 degrees F (0.7 degrees C) warmer than average, and 2005 was the 13th warmest year since national records began in 1895.

In Alaska, the monthly temperature was 8.3 degrees F above the 1971-2000 mean, making this the sixth warmest December on record for the state. Overall for 2005, Alaska temperatures were much warmer than average, ranking as the sixth warmest year dating back to 1918 when records began. The last four years have been within the warmest six years on record for Alaska.

Unusual warmth in the southern Plains combined with a continuing lack of rainfall to create severe drought conditions across eastern Oklahoma, parts of Texas and Arkansas. For the year, many locations in this region received less than 70 percent of their average annual precipitation. Little, if any, precipitation fell during the last three months of the year, and October-December was the driest such period on record in northeastern Texas, southeastern Oklahoma and much of Arkansas. Daytime highs were in the upper 70s and 80s, with strong winds and extremely dry conditions. This led to extensive wildfires that destroyed homes and businesses and caused several fatalities in Texas and Oklahoma as more than 300,000 acres burned. This was part of a record-setting 8.6 million acres nationally lost to wildfire in 2005, according to preliminary data from the National Interagency Fire Center. (Click NOAA image for larger view of December 2005 state precipitation rankings. Please credit “NOAA.”)

By contrast, a series of strong Pacific storms moved across the West Coast in late December. The largest rainfall totals since 1997 occurred in many parts of northern California and Oregon, leading to damaging floods and mudslides. Snow fell in the highest locations of the Sierras, while rain fell in many mid-elevation locations that had received snow in early December. In a reversal of the dry conditions observed during the 2004-05 winter season, average-to-above-average snowpack levels covered northern Colorado to northern California and parts of the Pacific Northwest, producing a good start to the water year (Oct.-Sept.) for these areas.

Conversely, very dry conditions in the mountains of southern Colorado, New Mexico and Arizona left many locations with at-or-near record low snowpack at the start of 2006. More than 90 percent of reporting stations in Arizona, the most in at least 40 years, were snow-free Jan. 1. The West is heavily dependent on seasonal snowpack to fill reservoirs during the spring and summer melt season. The heavy snowfall in this region during the 2004-05 season has left many reservoirs at relatively high levels, which will help diminish impacts if this season's snowfall remains below average.

The 27th named storm in the Atlantic formed Dec. 30, the latest development of a tropical storm in the basin since the storm that developed into Hurricane Alice in 1954-55. Tropical Storm Zeta formed in the eastern Atlantic, and while never a threat to land, added one more storm to the list that exceeded the previous record of 21 storms in 1933.

GLOBAL
The average global temperature anomaly for combined land and ocean surfaces during December 2005 (based on preliminary data) was 0.70 degrees F (0.39 degrees C) above the 1880-2004 long-term mean. This was the ninth warmest December since 1880 (the beginning of reliable instrumental records), and the annual global surface temperature was near the record established in 1998. Although land surface temperatures were anomalously warm across areas that included the high latitude Northern Hemisphere, West Africa and parts of the Middle East and western Russia, cooler-than-average conditions were widespread across areas that included south-central Russia, the eastern U.S. and southern Europe. Neutral El Niño/Southern Oscillation conditions continued in the equatorial Pacific, although indications of a developing weak La Niña episode were highlighted by anomalously cold sea surface temperatures in the eastern equatorial Pacific.

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