Major Highlights
NOAA REPORTS DECEMBER A MONTH OF EXTREMES IN THE U.S.
GLOBAL TEMPERATURE WARMER THAN AVERAGE
The last month of 2005 began with unusually cold conditions across much of the nation and ended with record heat and wildfires in the southern Plains and strong storms in the Far West. The nationally averaged temperature for December was near average, with colder than average conditions in the Pacific Northwest and east of the Mississippi and warmer than average conditions in the Southwest and northern Plains. Precipitation was at near-record to 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 9th warmest on record. NOAA is an agency of the U.S. Department of Commerce.
NOAA scientists report that the average temperature for the contiguous United States for December (based on preliminary data) was 33.5°F (0.8°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 well into the southern U.S. A strong snowstorm (Category 2 on the Kocin-Uccellini Northeast Snowfall Impact Scale) moved across the Midwest and Northeast on December 8-9, and a damaging ice storm struck parts of the Southeast mid-month.
Atmospheric circulation changes during the last two weeks of the month brought a retreat of the Arctic air mass and put the U.S. under the influence of warmer air from the Pacific. Temperatures for the last week of the month were more than 15°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 US was 1.2°F (0.7°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°F above the 1971-2000 mean, making this the 6th warmest December on record for the state. The year was also much warmer than average for Alaska, ranking as the 6th warmest since statewide records began in 1918. The last four years have all been within the warmest 6 years on record for Alaska.
Unusual warmth in the southern Plains combined with a continuing lack of rainfall to create severe drought conditions across large parts of eastern Oklahoma, north-central to southern Texas, and Arkansas. For the year, many locations in this region received less than 70% 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 in the upper 70s and 80s, strong winds and the extremely dry conditions led to extensive wildfires that destroyed homes and businesses and caused several fatalities in Texas and Oklahoma. The acreage that burned across these states in December increased the nation's total number of acres lost to wildfire in 2005 to a new record of more than 8.6 million acres, according to preliminary data from the National Interagency Fire Center. Since the New Year, over 750 fires have been reported and over 400,000 acres have burned in Texas, Oklahoma and Arkansas, with many of these fires still affecting the region.
In contrast to the record and near-record dryness in the southern Plains, a series of strong Pacific storms moved across the California to Washington coast in late December. The largest rainfall totals since 1997 occurred in many parts of northern California and Oregon and led 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 conditions during the 2004-05 winter season, snowpack levels from northern Colorado to northern California and parts of the Pacific Northwest were generally average to above average, producing a generally good start to the water year (Oct-Sep) for these areas.
Conversely, very dry conditions in the mountains of southern Colorado, New Mexico and Arizona left many locations with record or near-record low snowpack at the start of 2006. More than 90% of reporting stations in Arizona were snow free on January 1, the most snow-free locations in at least the past 40 years. The West is heavily dependent on seasonal snowpack to fill reservoirs during the spring and summer melt season. Despite the heavy snowfall in this region during the 2004-05 season that left many reservoirs at relatively high levels, a continuation of warmer and drier than average conditions could adversely impact water availability in 2006.
The 27th named storm in the Atlantic formed on 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°F (0.39°C) above the 1880-2004 long-term mean. This was the 9th 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 in December were anomalously warm across Alaska, West Africa and parts of the Middle East and western Russia, cooler-than-average conditions were widespread across south-central Russia, the eastern U.S., and southern Europe. Neutral El Niño/Southern Oscillation conditions continued in the equatorial Pacific, although indications that a weak La Niña episode may develop in 2006 were highlighted by anomalously cold sea surface temperatures in the eastern equatorial Pacific.
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