To make forecasting even more difficult, Washington is between two regional climate zones: the Atlantic Ocean and Gulf Stream to the east, and the Blue Ridge and Appalachian mountains to the west. This creates a special transition zone, with warm air on one side and cold air on the other.

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The elevation change between the low-lying areas east of Washington and the high elevations to the west also plays a critical role in snowfall forecasts. It is more likely to snow in higher elevations simply because it is colder. Sometimes, just this slight deviation in temperature can make or break a forecast.

Below, we use a variety of winter storm types to illustrate four common scenarios: a big snow, a few inches, an ice storm and rain. As for the dreaded wintry mix? It can show up in any of the scenarios. Wintry mix is a catchall term meteorologists use. It means at least two types of precipitation will fall, and it will not be pretty.

THE BIG SNOW

The biggest snows and most ruthless blizzards are almost always caused by the kind of storm people know best: the nor’easter, named for the direction from which the wind blows onto the East Coast. A nor’easter feeds on moisture and heat from the warm Gulf Stream. If the storm tracks north very close to the Mid-Atlantic coast, a nor’easter can dump a boatload of snow along the Interstate 95 corridor.

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Notable storms

Jan. 22-23, 2016, Snowzilla, 17 to 30 inches

Feb. 5-6, 2010,Snowmaggedon, 18 to 32 inches

Jan. 6-8, 1996, Blizzard of 1996, 17 to 25 inches

Feb. 18-19, 1979, Presidents’ Day snowstorm, 16 to 26 inches

A FEW INCHES

The vast majority of the region’s snowstorms consist of a glancing blow – just a few inches but enough to wreak havoc. We see it play out every winter, often in the form of an Alberta clipper, which gets its name from the Canadian province where the storm tend s to originate. Clippers are cold enough to deliver snow if they track south of Washington, but they tend to be moisture-starved, so we don’t often see big snow totals from them.

THE ICE STORM

The D.C. region is particularly prone to ice because of its proximity to the mountains, which act as a dam for the cold air drifting in from the north. Subfreezing air pools near the ground so precipitation that might have otherwise fallen as rain becomes supercooled and freezes instantly when it makes contact with the ground.

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Notable storms

Feb. 10-11, 1994, up to 3 inches of ice

Feb. 14, 2007, Valentine’s Day storm, 4 to 8 inches of snow and sleet; up to 3/4 inch of ice

A COLD RAIN

All winter storms have the potential to wind up as a cold rain, given the right track. One type that stands out, though, is the “Appalachian runner.” This storm tracks north along the Appalachian Mountains, well west of Washington, which puts most of the Mid-Atlantic in the warm sector of the storm. Cut off from the cold air, precipitation may begin as snow or a wintry mix but quickly turns to rain.

Notable forecast “busts”

Dec. 26, 2010, up to 12 inches forecast, not one inch fell

March 6, 2013, Snowquester, 5-10 inches forecast, not one inch fell

THE REVERSE FORECAST BUST

The slightest variation in storm track can lead to another interesting type of bust: one where little or no snow is expected, yet as much as a foot ends up falling.

Notable reverse forecast busts



Jan. 25, 2000, forecast was rain, 9 to 18 inches of snow fell

March 9, 1999, forecast was rain, 8 to 12 inches of snow fell