Sunday, December 19, 2010

Hype-ocracy: White Christmas in Washington

In a town normally overrun with hype, the hyping of Washington snow on Christmas reaches even more extreme heights. With the event still 6 days away, the possibility of Washington snow on Christmas has once again appeared among the blogotariat and the ratings-driven media. The chances of Washington snow on Christmas was featured on at least 3 local TV channels (WTTG-5, WJLA-7, and WUSA-9) tonight; WRC-4 was delayed by the football game too late to make this survey.

In fact, this year the cold air is firmly entrenched, but that didn't prevent the earlier outlook for Washington snow [the week before] Christmas to be a complete bust today. Some previous indications of the white stuff for Tuesday have also trended strongly toward the bust-bucket. Nevertheless, some models are hinting at the possibility of a storm developing late in the week and bringing some Washington snow on Christmas.

Three years ago, CapitalClimate surveyed the climatological prospects for Washington snow on Christmas:
Climatologically, there is only about a 10% chance of 1" or more of snow on the ground on Christmas in Washington. Since 1929, there have been only 8 such occurrences. The largest amount was 7" in 1966, with 5" and 4" in 1962 and 1963, respectively. That was the only time it happened in consecutive years. The most recent was 1989, with 2". The wettest was 1.41" of rain in 1945.
Since that time, there has been one more year with Washington snow on Christmas. That was, of course, 2009, when 7" remained on the ground from the 16" which fell on the 18th-19th. That marked the first time there had been Washington snow on Christmas in 20 years. If there is Washington snow on Christmas again this year, it would be only the second time that had occurred in consecutive years since 1929.

As for Washington snow on Christmas resulting from measurable snow falling on the actual day of December 25, that's only happened 6 times in 81 years (7.4%), and only 2 of them were over 1". Here's the complete list:
1962 5.4
1969 4.3
1935 0.6
1970 0.3
1993 0.2
2002 0.2
Still dreaming of Washington snow on Christmas? The odds are certainly better this year than the climatological average, but tonight's glib pronouncement of a "50-50 chance" for Washington snow on Christmas by Washington novice Anny Hong on WUSA, Channel 9, was waaaay premature.

Image (click to enlarge): Washington snow on Christmas (amount falling on December 25) since 1929; CapitalClimate chart from NWS data

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