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Posted at 11:37 AM ET, 01/18/2012

D.C. long-term snowfall still in decline


Graphic by CWG’s Steve Tracton (embedded photo by Ian Livingston)
Joel Achenbach, one of the Post’s most gifted writers, did a great piece today about this year’s lack of snow. Check out this attention-grabbing opener:

This has been a winterless winter, a season that can’t make it past lunchtime without busting out in a springtime melody. Every time cold weather shows up, it catches a flight back north the next day. Snow this year is a thing of myth and legend.

He cites me in the article, noting:

Snow has become gradually scarcer in the Washington region in recent decades, according to an analysis by Jason Samenow of The Post’s Capital Weather Gang. Average annual snowfall at the region’s three major airports has been declining by roughly an inch per decade, Samenow found.

So what about that analysis?

You may recall I did a blog post way back in 2008 that concluded: “average seasonal snowfall has been dropping and dropping fast over the past 120 years.”

In a follow-up post, I investigated the cause of the decline, and speculated it had to with a trend towards a more positive North Atlantic Oscillation (NAO). A positive NAO favors fewer big dips in the jet stream over the Eastern U.S. and hence cold air outbreaks and the potential for snowstorms.

Of course, since then, we had a highly negative NAO and the record-setting Snowmageddon winter of 2009-2010. Did that change the tendency of the long-term snowfall trend?

Not really.


The moving 30-year snowfall averages at the three area airports compared to the moving average of the North Atlantic Oscillation index during winter (Dec-Jan-Feb).

If you examine data at the three local airports through 2010-2011, i.e. Reagan National (DCA), Dulles (IAD), and Baltimore Washington International (BWI), the snowfall trend remains downward.

(Note: This particular analysis only includes snowfall data since the region’s observing stations have been situated at the airports. I did this to guard against bias introduced by changing observing station locations. So DCA’s record begins in1943, BWI 1950, and IAD in 1963)

Even after the record-breaking Snowmageddon winter, the rate of decline in annual snowfall at the three airports is the following:

Reagan National: 0.9”/decade
Dulles: 0.5”/decade
BWI: 1.5” per decade

The winter of 2009-10 only slowed the rate of decline by a couple tenths of an inch.

The trend for the NAO index, while averaging negative in both 2009-2010 and 2010-2011, also continues to be positive, but not as positive it was when I initially did the analysis. Of course, this year, it has averaged highly positive so far - so the downtick from the past two winters may reverse.

The bottom line is that snow continues to trend downwards and the NAO’s trend in the positive direction persists.

Until the NAO phase emphatically reverses course, snowfall will not mount a recovery. It doesn’t look like 2011-12 is going to help matters.

By  |  11:37 AM ET, 01/18/2012

Categories:  Local Climate, Latest

 
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