The holiday weekend is likely to get off to a snowy start in the D.C. area Friday night.
The National Weather Service has issued a winter weather advisory for most of the region Friday night and says to “plan on slippery road conditions.” A more serious winter storm warning is posted for northern Fauquier, northwest Prince William, Loudoun, Montgomery, Howard and Baltimore counties and points west. The Weather Service says “travel could be very difficult.”
The entire region could see snowfall rates of 1 to 2 inches per hour for a time between midnight and 5 a.m. under the heaviest snow bands, and visibility could be reduced to less than half a mile at times, the Weather Service said. There’s even an outside chance of thundersnow — when thunder and lightning briefly occur as flakes pour down.
Accumulation forecast
We’re forecasting 3 to 5 inches across our northern and western zones, including Northwest Washington. Precipitation of mostly or all snow and slightly colder temperatures in these zones should enhance snow accumulation. A few spots could top out around 5 to 6 inches.
We’re forecasting 2 to 4 inches around downtown D.C. and to the south and east, except only a coating to 2 inches in southern Maryland. In these zones, precipitation could start as rain or a rain-snow mix, and slightly warmer temperatures should keep accumulations down a bit.
Slight shifts in the forecast are still possible as new information comes in.
Storm timeline
9 p.m. Friday to midnight: Snow arrives from west to east, possibly starting as rain or a rain-snow mix around downtown Washington and to the south and east, and becoming moderate to heavy to the west. Temperatures: mid- to upper 30s.
Midnight to 4 a.m. Saturday: Snow could be moderate to heavy at times across the entire region, accumulating on roads. Temperatures: upper 20s to mid-30s.
4 a.m. to 6 a.m. Saturday: Snow tapers from west to east. Temperatures: upper 20s to low 30s.
6 a.m. to 10 a.m. Saturday: Improving road conditions on main roads and highways. Side roads could still be snowy or slick; lingering snow shower possible. Temperatures: low to mid-30s.
Temperatures described above will be lowest in areas north and west of downtown Washington and highest to the south and east.
Storm impact
The storm rates as only a low-end Category 2 out of 5 (and a Category 1 in our far-southern areas) on our Winter Storm Impact Scale. It’s occurring at one of the least disruptive times possible — in the middle of the night before a long weekend. And, outside of a lingering snow shower or two, it will be over by the time most people are waking up.
If you’re among the few to be on the roads between midnight and 5 a.m. Saturday, however, driving will be very hazardous because of the snowfall rates of 1 to 2 inches per hour and low visibilities. Roads will quickly become snow-covered and slick.
If you have Saturday morning plans, they may be disrupted until crews can treat and plow neighborhood roads, assuming you’re not comfortable driving on a bit of snow. We imagine major roads will be cleared pretty quickly Saturday morning. There could be delays and some cancellations at airports, so check your flight status before heading out.
By Saturday afternoon, snow will be steadily melting, and the area should be able to return to normal pretty fast. Lingering wet and slushy areas will refreeze Saturday night, so watch out for icy patches overnight into early Sunday. With highs well into the 40s on Sunday and sunshine, a lot of the snow will be gone by Sunday night.
How could the forecast go wrong?
There’s a pretty solid model consensus that most places, except areas south of Prince William and Prince George’s counties, should see at least 2 to 3 hours of moderate to heavy snowfall. However, amounts could end up on the low end of forecasts or in our “bust” range if precipitation intensity is a little lighter than simulated and temperatures are on the warm end of predictions. The risk of a bust is highest around downtown Washington and to the south, where above-freezing temperatures could eat into amounts. Also, if the snow moves through more quickly than forecast, that would also reduce totals. Some models show just a couple of hours of moderate to heavy snow.
On the flip side, amounts could end up at the high end of forecasts or in boom territory if the snow is on the heavy side of model predictions, which will cause temperatures to fall faster. Also, if the steady snow manages to linger a little later than 4 or 5 a.m. — when some models cut off — that could add an inch or so above the most probable amounts.
Expert analysis
“A quick-moving storm is likely to produce a narrow zone of particularly heavy snow Friday night. Where this band develops and stays in place the longest is where we could see amounts toward the high end of our snowfall forecasts, especially if it occurs in our typically colder locations north and west of the city,” said Wes Junker, Capital Weather Gang’s winter weather expert. “Areas that miss out on such a heavier band could see accumulations on the lower end of the forecast range, especially in our typically warmer locations from downtown D.C. to the south and east.”
