Monday, December 26, 2011

Yet Another Top-10 Warmest Year for Washington;
2011 To Rank 4th Highest in 141-Year Heat Parade

A balmy December is combining with the hottest month ever recorded to close out 2011 as the 4th warmest in Washington DC climate records dating back to 1871. Based on the December average so far of 45.1°, which is 4.7° above the 1981-2010 baseline, the yearly average of 59.9° will edge out 2010 by 0.1° to take the 4th position in the Washington annual heat parade.

Bumping 2006 into the 11th position, this year will take its place as the 5th year out of the last decade to be in the top 11 of all time. Three of the top 6 warmest years have now occurred in the 8 years beginning with 2004.

Projected temperatures for the remainder of this week, while above the seasonal average, will likely lower the monthly mean to 44.6°, but that will not be enough to change the yearly average. The projected average would make this month the 7th warmest December in history.

Indications for rest of winter?

As reported here 6 years ago, December temperatures are virtually uncorrelated with January's in Washington. However, looking just at the warmest Decembers, there is some indication that seasonal snowfall is likely to be below average. For the previous 10 warmest Decembers, the average total seasonal snowfall was 12.5", compared with a 1981-2010 average of 14.5". Only 3 out of the 10 seasons were above average. The highest was 27.6" in 1982-1983. Note, however, that 6.6" of that had already fallen in December, compared with a trace this year; the remainder occurred in February.

Images (click to enlarge): Top 10 warmest years and warmest Decembers in Washington DC; Total seasonal snowfall following warmest Decembers in Washington; CapitalClimate charts from National Weather Service data, background images © Kevin Ambrose (

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