The Washington Post

Friday night could bring round of sneaky snow

The percent chance of at least 1 inch (left), 2 inches (middle), and 4 inches (right) of snow between Friday night and Saturday night. We think these probabilites may be a little overdone for the D.C. area but are pretty reasonable overall. (National Weather Service)

A little storminess may develop along a cold front pressing through the region Friday night offering the next opportunity for rain and snow. Some snow accumulation cannot be ruled out but this is a particularly tricky situation to forecast.

There are a lot more questions than answers for this possible winter weather event, so it’s difficult to nail down details at this range. But here’s how, Wes Junker, our winter weather expert, sees the event unfolding:

This is another tough forecast. Precipitation will start rain during the evening with temperatures above freezing but could then transition to snow during the night. How much snow falls and accumulates will depend on the snowfall intensity and whether a heavier band sets up.

The highest snow accumulations are expected to the north and west where temperatures will be coldest but there may be more potential for heavy banding east and northeast of the city.

Right now, the best guess is for 1-3 inches in the colder suburbs and and coating to 2” in and around the city. However, if the system develops a little quicker and we get into a heavier band than amounts could be higher. Or, if no band of heavier precipitation develops, snowfall amounts could even be lighter

Two models show big differences in forecast snow amounts. The NAM (left) suggest generally 1 inch or less, with highest amounts north of D.C. The GFS (right) suggests 1-2 inches, with even higher amounts east of town. (

The reason the storm is especially difficult to forecast is because the wave of low pressure will be developing almost directly overhead. If it forms just a little earlier (to our southwest) or later (to our northeast) than forecast, that would result in higher or lower accumulation amounts.

“This is a bust waiting to happen,” Junker added.

With uncertainties this large, snowfall probabilities are best used in this situation.

No snow: 20 percent

“Car-topper” - conversational snow (up to a coating): 25 percent

Nuisance snow (up to 1 inch or so): 25 percent

Light snow (1-3 inches): 20 percent

Signficant snow (3 inches or more): 10 percent

This boils down to a 70 percent chance of 1 inch or less, and a 30 percent chance of something more.

We’ll try to sharpen forecast details further tomorrow.

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.

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