The Supreme Court building as Snowmageddon was winding down, February 2010. (Ian Livingston)

The ‘significant and strengthening‘ El Niño event in the tropical Pacific is on the cusp of attaining a rating of “strong”, which has happened only five times since 1950. The National Weather Service says this event is almost certain to last through the winter.

We keep getting the question, what does the strong El Niño mean for Washington, D.C. this winter?

During the five strongest El Niños since 1950, winters either featured among the most paralyzing snowstorms in Washington, D.C.’s history or hardly any snow at all.

Why such variation? El Niños tend to have two primary effects on U.S. weather which play out in complicated ways over the Mid-Atlantic: 1) They push the average position of polar jet stream north, which favors warmer than normal air over the region 2) They intensify the moisture supply along the southern jet stream, increasing the potential storminess.


(NOAA)

The combination of these two El Niño effects sometimes means D.C. gets flooded with mild air throughout the winter, favoring rain rather than snow when moisture-laden storms come along. But, at other times, just enough cold air hangs around for it to get hammered by a crippling snowstorm. (Whether there is sufficient cold air is often dependent on the state of the Arctic Oscillation).

Below I summarize Washington’s winter weather conditions during the five strongest El Niño events, revealing the wildly contrasting outcomes….

1957-1958: Strong El Niño, 40.4 inches of snow

From end to end, 1957-1958 was a blockbuster snow winter in Washington, D.C. A foot fell in December, over 17 inches in February, and over 10 inches in March. The winter was highlighted by the snowstorms on February 15-16 and March 19-21.

The mid-February storm dumped 14.4 inches of snow at Reagan National. “At the Bowie race track over 5000 people were stranded while the Pennsylvania Railroad sent rescue trains which were delayed many hours,” the National Weather Service writes.

The late March storm, a slow moving Nor’easter, laid down 4.4 inches at Reagan National but much greater amounts to the north and northeast. In sections of Baltimore and its north and northeast suburbs 20-30 inches fell. “Up to a million homes lost phone service and 2000 poles came down,” the National Weather Service writes. “300,000 homes lost electricity including the entire communities of Frederick, Annapolis, Aberdeen, Bel Air, and Havre De Grace. For many, it was over a week before power was restored.”

It was a colder than normal winter, with an average temperature of 35.7 degrees (compared to the 1981-2010 normal of 38.1 degrees).

1965-1966: Strong El Niño, 28.4 inches of snow

The winter of 1965-1966 was a snowy one, although the snow concentrated in January and February, when 21.3 inches and 6.9 inches fell, respectively. The storm of the winter occurred January 29-30, when 13.8 inches fell, on top of 6 inches already on the ground. “Intense blowing and drifting snow continued [after the storm] and kept roads closed for several more days crippling transportation lines and causing a food shortage and rationing,” the National Weather Service writes.

It was a slightly colder than normal winter, with an average temperature of 36.7.

1972-1973: Strong El Niño, 0.1 inches of snow

Washington, D.C. was practically shut out of snow in the winter of 1972-1973, with just 0.1 inches measured in February at National Airport. Modestly more snow fell north and west of the District. Dulles Airport recorded 2.2 inches, scattered over 6 months (0.1 inches in October, 0.6 inches in November, a trace in January, 0.3 inches in February, 0.2 inches in March, and 0.1 inches in April). This must have been a very frustrating tease of a winter for snow lovers.

Temperatures were slightly above normal, with an average temperature of 39.4

1982-1983: Very strong El Niño, 39.2 inches of snow

In what was the second most intense El Niño event on record, it was a mild winter in Washington with an average temperature of 40.8 degrees. There were long snowless stretches, but the winter delivered an impressive seasonal snow total of nearly 40 inches thanks to big storms in December and February.

[How the super El Nino of 1982-83 kept itself a secret]

A storm on December 12 dropped 6-10 inches of snow over the region, but – by far – the winter was defined by the blizzard on February 11-12, which paralyzed the region after unloading 16.6 inches at Reagan National Airport. “For a couple hours of the storm, snow fall at an amazing rate of 3.5 inches per hour,” the National Weather Service writes. “Thunderstorms intensified the snowfall in some areas.Winds gusted over 25 mph all day on February 11 causing drifts up to five feet.”


Snowfall during the blizzard of 1983 (NOAA)

1997-1998: Very strong El Nino, 0.1 inches of snow

The strongest El Niño on record produced a warm and virtually snowless winter in the District. While Reagan National only received 0.1 inches in December, Dulles Airport, managed 5.9 inches of snow over the course of the winter (4.7 inches in December, 0.5 inches in January, and 0.7 inches in February)

The average temperature was 42.5 degrees at Reagan National, several degrees above average.

Look ahead

In three of the five big El Niño winters, blockbuster snowstorms (3 of the top 15, and 2 of the top 10 biggest on record) brought the D.C. area to a standstill while basically no snow fell in the other two. A sample size of five is an impossibly small sample size to project what will happen this winter with a strong El Niño likely in place.

All we can say is that we’ll have elevated chances of getting hit by a really big snowstorm given an intensified southern jet stream, but that’s only if cold air is around.

[Will El Niño bust or bolster D.C.’s snow prospects? A way too early look at next winter]

It should be a very interesting winter.