Friday, December 18, 2009

Washington DC Snow Freqs: December Records

For related and more recent posts, see:Generations of Washington area snow freaks have learned the hard way not to count their flakes until they're baked, but all indications are that a Big One is cooking in the kitchen of Momma Nature's Weather Grill. The latest National Weather Service forecast, updated within the hour, is calling for total snow accumulations of 14-16" by Saturday night. Stu Ostro of The Weather Channel has his usual excellent analysis of the storm here:
It's as easy as A + B = C.

In order to see how big the forecast amount really is, Momma's data dicers dusted off a chart originally published three years ago. Including the two trace amounts and 2.6" recorded in the meantime, the fraction of years with no measurable December snow now stands at 23% for the 121 years since official records began in 1888. Only 11 times (9%) have monthly totals exceeded 10". The most recent occurrence was in 1973 with 11". The others were:
1962 16.2"
1966 16.1"
1932 14.5"
1904 13.2"
1890 13"
1910 12"
1957 12"
1908 11.5"
1935 11"
The 1973 amount consisted mainly of 6" on the 16th and 4.2" on the 17th. The last time 10" fell on a single calendar day was Dec. 4, 1957 with 11.1". Since records began at the current National Airport location in 1929, there have been only two other December days with 10" or more: the 26th in 1941 (10") and the 17th in 1932 (11.5"). The 11.5" in 1932 holds the all-time December daily snowfall record. Of the 12 heaviest 3-day snow totals (12.7" or higher), none have occurred in December.

Images (click to enlarge): Precipitation forecast from The Weather Channel;
CapitalClimate chart from National Weather Service data, photo © Kevin Ambrose;
Energy and math symbols holiday snowflakes from MIT, animated version here.

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