December marked the 11th warmer-than-normal month of the 2012 calendar year and helped cement Washington, D.C.’s 2012 status as the warmest year on record. The month closed as the sixth warmest December on record.
It was just 0.3 degrees cooler than the record warmest Decembers of 1889 and 1984. Another very warm day or two could have pushed the month over the top. Through 2012, 50 percent of the warmest Decembers occurred in either the 1990s or 2000s.
The average temperature of 45.3, 5.6 degrees above the 1981-2010 normal, was very close to 2011’s 45.0 degrees. Comparing December 2011 and 2012 side-by-side, we see they had the same lowest temperature for the month, but 2012 had some much more impressive peak temperatures (70s!).
In terms of daily weather, the “red” warm days outnumbered the “blue” cold ones by a huge margin.
From a records standpoint, Washington Reagan National saw two for temperature: a high temperature record on December 3 (71F), and a record warm minimum on December 17 (48F).
Compared to other years, the precipitation total fell in the middle of the pack but totals were quite a bit lower than last year. While we had some wet days, they were primarily found in the second half of the month. National only recorded .2” of snow vs. a 30-year normal of 2.3”.
Reagan National and Dulles Airport set daily precipitation records on the 26th. Dulles even picked up a daily snowfall record on the 29th (0.9”).
Prevailing weather pattern
The prevailing jet stream pattern is a lesson about how there are many meteorological ways to come up with the same result. The North American pattern was quite different from last year in a lot of key areas, but we still were in the same general ballpark as last year’s monthly temperature result.
This year, we saw more high pressure in the upper levels over the Greenland area. Normally, that pattern type favors cold conditions in the Eastern U.S. (as we saw in November actually). But here in December, the bigger power player was that cold upper level low/trough over Western Canada. That feature helped keep a warm pattern in place farther to the east over our area (think of it like a see-saw: when it goes cold there, it has to go warm here). Last year, we had a cold pattern over Greenland with a prevailing jet stream pattern that kept all the cold air bottled up in the high-latitudes instead.
A look ahead
The National Weather Service is forecasting January to be warmer than normal despite our seasonal to slightly colder than normal start to the month. The latest pattern idea is that by next week, we should be experiencing a thaw in the pattern with highs back into the 50s with even a chance toward the low 60s by two weekends from now. Colder pattern shifts are possible either mid- or late month.
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly)
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