The northern end of the Northeast megalopolis lies in the proverbial sweet spot for snow, as general observations have shown over the years. A closer examination of the historical record reveals not only increases in the seasonal snowfall totals for Boston and New York City, but also unearths this all too predictable truth: Maryland and Virginia winters are becoming less snowy.

Data obtained from a variety of sources – National Climatic Data Center reports, NWS forecast offices and the Franklin Institute, to name a few – point at the disparity in snow fortunes.

Boston Logan Airport and La Guardia Airport (New York City) have have, generally, experienced increasing seasonal snowfall since the 1980s, while Baltimore-Washington International Airport, Reagan National Airport and Richmond International Airport have all seen substantial declines. Philadelphia International Airport has experienced a less discernible decreasing trend.

This analysis begins at the winter of 1948-49 because this is the latest full seasonal period from which any of the airports had begun to take observations (Philadelphia holds this distinction). Records stretch as far back as the 1930s at the Boston and Richmond airports, but I chose to chart the trends since 1948-49 to provide an even comparison.

Now, for some hard numbers: Boston’s average seasonal snowfall has risen from 42.3 inches in the period ending 1979-80 to 43.7 inches in the three-plus decades since. In New York, the increase is more pronounced; the average amount of 23.5 inches in the earlier period has shot up to 26.4 inches since 1980-81.

The Mid-Atlantic has witnessed opposing trends. Washington, D.C., for example, received an average of 17.4 inches from the late 1940s through the late 1970s, but since the 1980s, the District has seen only 14.4 inches per winter. Baltimore’s snowfall decline is almost equivalent at two-and-a-half inches, sinking from 21.4 inches to 18.9 inches. Richmond bests both cities, having had its seasonal snowfall tumble from 15.2 inches to 9.6 inches.

Boston and New York’s post-1979 snowfall averages are beating their long-term (since 1948-49) means of 43 inches and 25 inches, respectively. Philadelphia (long-term mean of 21.7 inches; post-1979 average of 21.5 inches), Baltimore (long-term mean: 20.2 inches), Washington, D.C. (long-term mean: 15.9 inches) and Richmond (long-term mean: 12.4 inches) are not.

One can view other telling trends, specifically those related to individual snow events. I grouped each event since 1948-49 into four accumulation tiers: 1-3 inches, 4-6 inches, 7-11 inches and 12+ inches. (These ranges prevent overlap between events, as a reported total of anywhere from 3.1 to 3.4 inches, for example, rounds down to 3, while any amount between 3.5 to 3.9 inches rounds up to 4. The same does not apply for totals less than one inch. I did not round up from a 0.5-0.9 inch event).

At the lowest tier (1-3 inches), the average number of events per season declines across the board. The trend is strongest at New York, where a little over four such events occurred per winter from 1948-49 to 1979-80; since 1980-81, that number has averaged around 2.7. Washington, D.C.’s event average had sat just above three, but in recent decades, the mean has registered barely above two.

The same general decreasing trend holds at the next tier (4-6 inches), with Philadelphia posting the largest drop from 2.1 to 1.4 events per winter. New York is the only city that posts a countervailing trend, however. Its event average rises from 1.5 in the 1948-49 to 1979-80 period to 1.8 in the 1980-81 to 2012-13 period. Never before has Baltimore recorded three consecutive winters (2010-11, 2011-12, 2012-13) without a 4-6” event. Richmond actually endured a longer consecutive stretch (six winters) without a 4-6” event from 1996-97 to 2001-02.

Though the frequency of light-to-moderate snow events is waning in snow-prone Boston and New York, heavier snowfalls are increasing on average. Herein lies the explanation for why seasonal totals have shot up over the last 30-plus years: heavy snow storms (subjectively defined as 7 inches or more) are occurring with greater frequency over the coastal Northeast. Consider, for instance, that the average number of 7-11” events in Boston has risen from less than 1.7 to more than 1.8. New York’s mean number of about one 12”+ event per winter has, over the past 30 years or so, inched up toward 1.2.

What’s more, Boston has recorded four or five individual 7-11” events in four winters (1992-93, 1993-94, 1995-96 and 2007-08) since the 1992-93 season; only once before (in 1987-88) had the city experienced a winter with four or more such events. Furthermore, foot-plus events have occurred in seven of the past 11 Boston winters (since 2002-03); there is no comparable stretch in the city’s record since 1948-49. New York has also experienced an extreme snowfall bonanza, recording eight foot-plus events in the past 13 winters (since 2000-01). This is even more stunning given the fact that LaGuardia airport had posted only nine such events from 1948-49 to 1999-00.

The frequency of foot-plus events has also increased in Baltimore and Washington, D.C.. However, there is a much smaller sample size of such events in the District (9) and Baltimore (16) compared to that in Boston (33). Among the larger sample of 7-11” events in D.C. and Baltimore, the numbers are decreasing rather markedly,within the 1948-49 to 1979-80 period

I have already documented the major drop-off in 1-3” events for D.C., but the city is not alone when it comes to less frequent light snows. Before 1980-81, Baltimore averaged a little over three minor snowfalls per winter, but that average has shrunk to barely more than two in the last three decades. Richmond’s mean number of 1-3” events has fallen from around 1.7 within the period spanning the late 1940s through late 1970s, to near 1.3 since the early 1980s.

All these figures underscore the importance, at least in recent years, of heavy snowfalls. The long-term decline of light and moderate snow events across the Northeast megalopolis makes it difficult for cities along the I-95 corridor to reach their seasonal averages each winter, though Boston and New York are proving that it can be done with a surge of foot-plus accumulations.

A future post will address the impact of El Nino Southern Oscillation (ENSO) on these seasonal snowfall totals and the frequency of tiered events. Some have said that El Nino is a primary driver of snowier Northeast winters; I will investigate this claim.

Related posts:

How global warming spoiled the Snowquester

Does the “less snow, more blizzards” global warming theory hold up in Washington, D.C.?