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Posted at 10:00 AM ET, 11/25/2008

In Focus: Local Snowfall Trends

By Jason Samenow

* A Blustery Day: Full Forecast *

In last week's Winter Outlook, we wrote about the long term downward trend in snowfall in the District. Some of our more astute readers pointed out the District's "official" observing station -- located at Reagan National Airport -- has not always been located there, but moved from a location downtown; therefore calling into question the integrity of the long-term trend. We were also questioned about the fact we analyzed the snowfall trends at just one station. These points and questions were quite valid, so I did new analysis to address them. After doing so I've concluded the story hasn't changed: snowfall totals are still declining in our region.

Keep reading for more on the analysis...

Running 30-yr snowfall averages for Reagan National (DCA), Dulles (IAD), and Baltimore-Washington International (BWI) airports.

Prior to the winter of 1943-1944, the official observing station that's now Reagan National Airport (DCA) was located at 24th and M St. So, one might be tempted to argue the drop in snowfall was mainly due to the re-location of the airport due to the warming influence of the Potomac River and lower elevation. However, the moving averages indicate snowfall declined not only before but also well after the station was moved to the airport. In fact, when we examine the trend in the moving 30-year averages since 1973 (shown above) - which includes only airport data (starting in 1944) - we find a decrease in snowfall at DCA at the rate of about 9"/century.

The story doesn't change when we analyze Dulles Airport (IAD) and Baltimore-Washington International Airport (BWI).

While IAD's record is short (starting in 1963, so we only have 15 years of 30-year moving averages), its running snowfall average is declining at a rate of about 6.3"/century.

Like DCA, BWI took over weather-record keeping from the downtown observing station in 1951. And BWI's 30-year moving snowfall averages also indicate a declining snowfall trend. Since 1980, the 30-year moving average (encompassing snowfall data starting in 1951) has been falling at the rather astounding rate of 17.6"/century.

The bottom line is that regardless how we analyze local snowfall records -- whether we use parts of records (using a single observing location) or all of records (combining different observing locations), 15-year averages or 30-year averages, fixed or moving -- we're seeing declines that are most likely real.

By Jason Samenow  | November 25, 2008; 10:00 AM ET
Categories:  Local Climate  
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Next: A Cold Snap Fiercer Than Recent Januarys


Jason, by visual inspection it seems that the 30 years avg began to drop in the mid to late 80s or so. How does this correspond to the PDO and AMO cycles?

Posted by: mciaram1 | November 25, 2008 10:51 AM | Report abuse


Great question and great topic for a follow-up post. I was thinking about looking at correlations with temperature trends but the patterns you mention would also be interesting to investigate. I'll see what I can put together for this time next week...

Posted by: Jason-CapitalWeatherGang | November 25, 2008 11:04 AM | Report abuse

Bring on global warming!

Posted by: suntan | November 25, 2008 11:13 AM | Report abuse

West Springfield (Accotink Lake/Mixing Bowl): Rainfall total yesterday and this morning = 0.81"

That's more than I expected!

Posted by: bikerjohn | November 25, 2008 12:50 PM | Report abuse

I live in Culpeper Va and 100inches in a season couldnt be enough for me! but..around here its like pulling teeth just to get 5 inches anymore. I know there have been a fair amount of people calling for an average to above average snowfall for our area and I just don't see that happening. So far its been cold for November but dry for the most part and IMO December will be no different. We are not in a snowpattern by any means although I think its a cycle we are going through but the question is how long will it continue to be this way?

Posted by: clintonportis17 | November 25, 2008 5:37 PM | Report abuse

I live in Frederick MD and have spent a lot of free time pouring over climatalogical data myself. If you look at outlying areas like Hagerstown, you get a much different conclusion. In fact, since the early 70s, you can see a clear upward trend in the 10 yr moving average for annual snowfall for Hagerstown. Albeit a slight trend from ~23 to ~27 inches... it stands in stark contrast to the Capital Weather Gang's findings. See the following link:

There may be other explanations for the downward trends for DC/Baltimore. Something other than the commonly assumed global warming.

Posted by: Hokiefan314 | November 26, 2008 2:55 AM | Report abuse

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