This most recent drop in Washington’s snowfall will become official when the National Oceanic and Atmospheric Administration releases its new 30-year “climate normals” in May, its decadal update of average weather conditions for every location in the United States.
While NOAA hasn’t finalized D.C.’s snowfall numbers, they’re easy enough to calculate. Below, we preview what they’re expected to show and discuss their implications. (Note, minor discrepancies between our numbers and NOAA’s final numbers are possible due to differences in analysis methods.)
Losing snow across much of the winter season
Examining how the most recent 30-year averages have changed by month, our story of snow loss begins in November and ends in February. March is the only month that shows an increase when bringing in the new numbers from the past decade (2011 to 2020).
New monthly snowfall averages for the District, based on the period 1991 to 2020, are below, with the old period (1981 to 2010) in parentheses:
- November: 0.1 inches (0.5 inches)
- December: 1.7 inches (2.4 inches)
- January: 5 inches (5.5 inches)
- February: 5 inches (5.7 inches)
- March: 2 inches (1.3 inches)
December and February showed the greatest snow loss, each shrinking 0.7 inches. While January and February are now technically tied for Washington’s snowiest months of the year, February still has a slight edge when you consider it has fewer days.
Part of a long-term trend
Considering Washington typically saw about 20 inches of snow per winter around 1900, the city has lost about a third of its snowfall over the past century or so.
Reasons for long-term declines in snowfall are numerous but are closely tied to the rising winter temperatures, which have eaten away at amounts, particularly early and late in the season when it’s frequently only marginally cold enough for snow.
Even since the mid-1940s, when snowfall measurements moved from downtown Washington to Reagan National Airport, the average snowfall has fallen from about 18 inches to under 14 inches.
Snowfall declines also seen at Dulles and in Baltimore
The new averages show losses in snowfall at Dulles International Airport and Baltimore-Washington International Marshall Airport, as well.
At Dulles, every month (including April!) except March saw declines. The seasonal average there fell from 22 inches to 20.9 inches. Baltimore’s average fell 0.7 inches, from 20 inches to 19.3 inches, also showing losses in all months but March.
More broadly in the Mid-Atlantic and Northeast, our analysis of the data shows the loss of snow appears most pronounced in areas farthest south and at low elevations where temperatures are frequently only marginally cold enough to snow. In these areas, even small amounts of climate warming lower snowfall amounts, especially in winter’s shoulder months.
For instance, trends in places like Richmond and Norfolk are similar to Washington. Only midwinter tends to show relative snowfall stability in recent decades, whereas snow early and late in the season is vanishing.
To the north, these colder locations will need to warm up some more before long-term warming becomes a problem for snow accumulation. In Philadelphia and Hartford, Conn., for example, snow averages are up.
Is March the new winter?
As noted above, March is an exception when it comes to Washington’s diminishing snow returns. Whereas all prior months showed a decrease in the average, March numbers are up.
Washington’s March snowfall average is now about 2 inches, compared with 1.3 inches last averaging period. At Dulles, it’s up to 3.9 inches from 2.8 inches. And, in Baltimore, March snowfall climbed from 1.9 inches to 2.8 inches.
While March does regularly include accumulating snow, the change here is largely driven by a few recent snowy years like March 2014, when 12.7 inches fell in Washington.
Because March tends to offer less in the way of reliable snow than other winter months, it might not take as much to move the average, but our new March average is still the highest since the 1951-1980 period, when 2.9 inches was the expectation.
But looking at the longer term, the story for March still resembles other months. March average snowfall has fallen from about 4 inches at the start of the 20th century to the 2 inches today.
Historically, it becomes rare for accumulating snow to occur after around March 25 in Washington. While it’s not unheard of to see flakes into early April, the clock is ticking louder by the minute.