January 2010 Temperature Review: "Most Average" Since 1987

The new decade began with a cold first 2 weeks in the Washington DC area, followed by a warmer 2 weeks. A cold last 3 days brought the average of 35.3° for January 2010 down to within +0.4° of the 1971-2000 normal. This marked the 5th out of the last 6 years in which January has been above average. In the 11 years beginning in 2000, 8 have been above average. This January's average was also the closest to the long-term mean since 1987, when temperatures averaged just 0.2° below what is now the current normal. In fact, 2010 is tied with 1956 (-0.4°) for 11th closest to average out of 140 years of data.

There were 23 days with lows of 32° or below, and 6 of these failed to reach a high above freezing. These were a little more than the normals of 20.7 and 4.6, respectively.

Heating degree days totaled 914, just 0.3% below average. For the season the total is 2341, 2.5% below average.

Despite the frenzy of the snow obsessive-compulsives, the only statistic which really stands out for this January is the precipitation deficit. Following an excessively wet December, the year is starting out at less than 50% of average. The preliminary total of 1.36" may have to be revised upward, however, as December's was. The reported 0.13" of liquid associated with 6.4" of snow on the 30th would imply an astonishingly high ratio of over 49:1 of liquid to frozen precipitation. Including the measly 1" of powder which fell on the 8th, the total snowfall was only a little more than 1" above average.

Images (click to enlarge): Washington DC temperature departures from average, daily Jan. 2010, monthly 2000-2010 and 1871-2010; CapitalClimate charts from National Weather Service data