By: Phil Arkin
I’ve been a fan of snowstorms since I can remember, probably because I grew up in the Willamette Valley of Oregon where significant snow is a once-per-decade event (at least there was one storm of consequence in the 10 years that I remember). I moved to Silver Spring in June 1961 and rewarded with consistently snowy winters – the 60s averaged almost 2’ per year at National airport (DCA). Occasionally we would have a winter without much snow, but it was rare to get two in a row. Last year (snow years go from July to June, so last year was 2011-12) totaled 2”, and so far this year DCA has had 1” (you can get local climate information here).
If this goes on, we will have two consecutive very unsnowy winters, and I decided to see whether this has happened before. Before I tell you what I found, however, I should mention that we have a winner (well, sort of) in the ESSIC Snow Pool, part 1 – when will the first 1.0” of snow fall at DCA. Since we have not yet had a single such event this season, the winner is Gary Partyka, who forecast January 23, 2013, which was later than anyone else forecast. Some consideration was given to declaring a “no contest” if the winter ends without any 1” events, but we finally decided to award the prize1 to Gary. The seasonal total prize will have to wait, of course, although Augustin Vintzileos is looking good so far. This affair has been enjoyable enough that we will try it again next year, but considering the DCA “snow hole” and our location in College Park, I think that we will use BWI (Baltimore Washington Airport) next year.
Back to snow drought years: looking over the annual totals from 1888 to last year, a total of 124 years, I see 32 years (26%) with less than 10” and 13 (10%) with 5” or less. The chances of having two consecutive years with less than 5” in each should be 1 in 100 (as long as each year is an independent event), and that’s never happened so I guess we’re due! (I realize that’s not true – no need to write and tell me.) Three consecutive low snow years would be much more unusual, unless there was something going on in the climate to weight the odds. 😉
Actually, the distribution of snow events seems to be highly non-normal, and so simple guesses like these are unrealistic. Since I’m working from a monthly time series I can’t see individual events, but it is interesting to look for high monthly values – it has been speculated that the increasing atmospheric moisture associated with warming temperatures might lead to heavier precipitation events, and so fewer but heavier snowstorms. Unfortunately, the variation in decadal totals of high monthly values doesn’t seem to tell us much about that – every decade but two has 1 or 2 months with more than 20 inches, and the number of months per decade with more than 10” ranges from 3 to 9 but with no obvious trends. There might be some tendency for the very snowiest months to have occurred in the past 20 years – snowiest December (2009), 3rd snowiest January (1996) and 2nd (2010) and 4th snowiest February – but nothing I’d care to stand behind. Fun with numbers!