December shows unusual temperatures

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By Scot Johnson

Surprisingly, December was warm, as was 2010 overall.
The incredibly cold temperatures we experienced around New Year’s Eve and Day make it hard to believe, but December was quite a bit warmer than average.
The average temperature in Los Alamos and White Rock was 35 and 34 degrees, respectively, where 29-and-a-half is the norm for December in both towns.
The Los Alamos average for 2010 overall was 49 degrees, half a degree warmer than the 1981 through 2010 average.
The first two weeks of December were dry but pleasant with daytime highs of around 50 degrees and lows around 30, about 10 degrees above normal.
We grew accustomed to the idea that La Niña was pushing all the cold and wet weather to the north, and so we began watering our trees.
The storm that came on Dec. 16 shattered the mild conditions, reminiscent of a few cold fronts in November.
Temperatures plummeted to normal values and we received about 6 inches of snow that Thursday, shutting down Los Alamos National Laboratory the next day.
Dry weather returned and temperatures climbed to provide an unseasonably comfortable winter break. But then a massive system of cold air and moisture arrived from the Pacific Northwest on Dec. 29.
Los Alamos received about 9 inches of snow between the night of Dec. 29 and early afternoon on Dec. 30. And following the storm were temperatures so low that they are not likely to be matched for quite a while.
Temperatures bottomed out early on New Year’s Day at -9 degrees in Los Alamos. It has not been that cold since December 1996 when a low of -11 was recorded.
The all-time low in Los Alamos is -18 degrees. White Rock reached -10 degrees early on New Year’s Day, for the first time since December of 2004.
The all-time low in White Rock stands at an amazing -29 degrees, recorded on Jan. 6, 1971 and again on Jan. 7.
The precipitation total for Los Alamos was 20 percent above normal at 1.2 inches (liquid equivalent). White Rock collected an inch, also 20 percent above normal. The Los Alamos total for 2010 was 18.8 inches, very near the normal 19 inches. White Rock’s total of 13.5 inches was a bit below the normal 14 inches there.
The definition of normal conditions has now shifted from the average of 1971 through 2000 to 1981 though 2010.
The difference, of course, is that we replace 70’s weather with the most recent decade. The Los Alamos average annual rainfall has changed slightly from 18.95 inches to 18.97 inches. The 30-year average temperature has climbed from 47.9 degrees to 48.4 degrees.
La Niña is expected to remain in place during winter. The overall forecasts through spring include warm and dry weather, and this reflects the expected effects of La Niña. The forecast for January, however, is for a break in this trend with normal temperatures and a wetter than normal conditions.
Editor’s Note: Scot Johnson is a meteorologist for the Waste and Environmental Services Division, Environmental Data and Analysis Group at Los Alamos National Laboratory.