Is April snow in D.C. becoming more rare?
* Sun today, chance of rain tomorrow: Full Forecast *
Despite the early-April warmth (and maybe to spite people who consider it a four letter word) some snow lovers can't ever get enough. So before we put to bed discussion of snow chances 'til 2010-11, let's take a look at what April typically has to offer metro region snow hounds.
By the books, April provides close to nothing in the snow department. Nonetheless, snow does occasionally stick in April and an analysis of the stats tells an interesting story about its characteristics and long-term trends. One conclusion of my snow analysis is that snow of any consequence (of say, at least an 1") has always been fairly rare in the D.C. area during April. And quite interestingly, another conclusion is that April snow might be a dying breed, at least in the city itself.
Keep reading for an in-depth look at April snow stats... Do you like snow in April?
Snow has accumulated during April in Washington, D.C. 20 times since authentic records began at the start of 1888. By comparison, there have been around 150 in March and only 3 in October. Of the 20 events, one began in late March and dropped marginal additional accumulation in April. Another April event (of 1") is noted in the pre-authenticated snowfall records during the winter of 1886-1887.
The month's largest accumulation event occurred near the tail end of the "April-snow heyday" (keep on reading for more on this) when a brief but unusually cold air mass dropped into place ahead of a clipper-type system that eventually re-formed off the North Carolina coast early on April 1, 1924. The storm rapidly developed, heading from North Carolina to Maine by the morning of April 2, and dropped heavy spring snow across the interior northeast. Around 5" of snow fell in D.C. and other parts of the area, with some heavier amounts reported.
Seven other events greater than 1" have occurred in April. But no event since the 1924 storm has been able to surpass 1" in the city. Snow has fallen twice during the same April in only two seasons on record, 1897-1898 and 1906-1907.
A comparison of the past five decades and the first five decades of records (post 1880s, since data on the 1880s is quite incomplete) seems to indicate that we are either in a prolonged April snow drought or that April snow is in jeopardy of being moved from the endangered list to the extinct list here in Washington. The 1890s through the 1930s saw fourteen April events.
During the April-snow heyday, when "big" springtime snowfalls were more common, 5 events over less than a decade produced 15.3" of snow from 1915-1924. Every April from 1915 through 1918 featured an event with over 1", two of which were 3"+. By comparison, the last three accumulating snows at National -- all occurring on April 7 strangely enough -- happened in 2007, 1990 and 1972, combining for a paltry 1.2" of snow.
The "return rate", or length between accumulating events, in April has grown as the frequency of events has dropped. 14 events through 1923-24 produced an average wait between accumulating April snow of 3 years. Since 1924, the 6 events have come about once every 14 years. In today's "why is National destroying our snow records world?" it is worth pointing out (yet again) that the downward trend in event numbers showed up prior to the snowfall observation location being moved to the airport during the 1940s.
The story is a little different to the north and west, however. At Dulles (IAD), for example, the frequency of April snow is not much higher than National but it has been able to record 1" or more of total April snow 4 times going back to 1972-73 (while neither National or Baltimore-Washington have done so). April's most notable example (since IAD records began in the 1960s) of the "interior advantage" came during 1990 when IAD recorded 4" of snow compared to National's 0.2" and BWI's 0.1".
In summary, the evidence for declining April snow in Washington is compelling but perhaps inconclusive. Urbanization along with possible climate change effects on the entire globe are all likely playing a role. It is also possible the April snow heyday was a blip, an anomalous period in time when April events happened more frequently simply by chance. Any observation location is of course just one spot on a large map, and late-season events can have numerous micro-scale differences that result in variable snow patterns.
Sources include NOAA daily records, official monthly and seasonal records posted on NWS Sterling's Web site and other NOAA archives like the Daily Weather Maps project. Ian is co-author, with Kevin Ambrose, of the forthcoming "Great Blizzards and Snowstorms of Washington, D.C." The book will be available by late 2010 or early 2011.
| April 12, 2010; 10:30 AM ET
Categories: Local Climate, Winter Storms
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