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Winter storm late Sunday to bring snow, ice and rain along with dangerous road conditions

Expect hazardous travel conditions Sunday evening in the D.C. area as snow changes to ice.

The Washington region is under a winter storm watch ahead of a Jan. 16 storm expected to bring snow, sleet and rain. Here’s what you need to know. (Video: Amber Ferguson/The Washington Post)
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* Winter storm watch from Interstate 95 westward Sunday afternoon to Monday morning *

10 p.m. — Forecast mostly on track but freezing rain threat increasing in our western areas some

Afternoon and evening forecast models generally support our snowfall forecast of between one and four inches in the immediate area (highest amounts west of D.C. and lowest to the east) Sunday afternoon and evening, as described below, before a change to a wintry mix. However, some models are showing a decrease in snow amounts and an increase in ice for our far western areas, generally west and northwest of Fairfax County toward Interstate 81. In other words, we may need to shave back the snowfall forecast a bit for those areas in our updates Saturday. But the threat of freezing rain and perhaps some power outages may increase.

Here’s a map of projected freezing rain totals from the high-resolution NAM model. If this model is right, the areas in the dark pink shades, where at least 0.25 inches is projected, may have some significant icing issues.

We’ll have our next forecast posted at 5 a.m. Saturday and a full, updated storm briefing midday.

3:10 p.m. — Winter storm watch expanded eastward to District and I-95

The winter storm watch, previously in effect only for the far western part of the Washington region, has been extended eastward to include the District and I-95 corridor.

In the immediate Washington area, the Weather Service is calling for 1 to 3 inches of snow, with up to 5 inches in a few areas, along with 0.1 inches of ice. It also cautioned wind gusts could reach 45 mph.

The watch includes Fairfax and Montgomery counties but not eastern Howard County, Prince George’s County, Charles County or locations to the east.

Original article from 1:15 p.m.

The forecast for Sunday’s winter storm is coming into focus, and it’s going to be one big mess in the Washington region.

Snow falling on frozen roads late Sunday afternoon and evening will make for treacherous conditions, with sleet and freezing rain adding a crusty coating into Sunday night. Then the frozen precipitation will change to plain rain overnight Sunday, leaving behind slushy slop for Monday morning.

We expect the worst travel conditions in the immediate area between about 5 p.m. Sunday and midnight.

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Snow accumulations in the immediate D.C. area may be only around an inch or two but will increase to the west. Toward Loudoun and Frederick counties at least 3 or 4 inches of snow could fall before a transition to ice.

As the storm progressively draws milder air from the ocean and casts it westward, areas east of Interstate 95 will have the shortest duration of frozen precipitation and difficult travel conditions, and areas closer to the mountains face a serious, long-lasting winter storm with heavy accumulation of snow and ice. At least 6 to 12 inches of snow could fall in the Blue Ridge, near Interstate 81 and in the Appalachians, with perhaps a glaze of ice as well.

Ahead of the storm Friday, outgoing Virginia Gov. Ralph Northam (D) declared a state of emergency. Especially in the far western parts of our region, the combination of snow, ice and gusty winds, up to 30-40 mph, could cause power outages.

Virginia governor declares state of emergency ahead of winter storm

Snow and ice amounts

Model trends suggest a rather short period of snow near and east of Interstate 95 — perhaps only a couple of hours — before a changeover to sleet and freezing rain, limiting totals. However, with freezing temperatures for at least 36 hours in advance of the storm, every flake that falls will stick to roads and walkways.

Generally, expect snow amounts to increase as you head west and rise in elevation.

Here’s how much different models project for the District:

UKMet: 3 inches | European: 2-3 inches | American (GFS): 2 inches | Canadian: 2 inches | NAM and high-resolution NAM: 1 inch

Weather Service warned VDOT of heavy snow threat ahead of I-95 disaster

Models have generally come down in their projected snow amounts since Thursday, as they suggest the storm will draw in more mild air at high altitudes. But because of the frozen roads ahead of the storm and the potential for ice on top of snow, we shouldn’t be lulled into complacency by the modest snowfall forecast. Roadways and walkways Sunday evening will most likely be very hazardous for motorists and pedestrians.

A few hours of sleet and freezing rain are possible in the immediate area after the snow, leaving behind a glaze of a tenth of an inch or so. In our colder areas north and west of the Beltway, some areas could even see a quarter inch or so of ice.

Because the push of mild air to the east will be strong enough to change the ice to plain rain after midnight, we don’t think power outages will be a big problem in the immediate area. However, we will monitor this possibility as winds will increase during the transition from freezing rain to rain, potentially causing limbs to snap. Power outages may be a greater concern where there is more ice accretion, particularly west and northwest of Fairfax County.

Storm timeline, temperatures and winds

Temperatures shown will be lowest in our northwest areas (toward Leesburg and Frederick) and highest in our southeast areas (toward Southern Maryland) through the course of the storm. Overnight Sunday, we expect a very large range in temperatures across region; it’s possible parts of southern Maryland warm to near 50 while temperatures in places like Leesburg and Frederick hover closer to freezing.

1 to 5 p.m. Sunday: Snow develops from southwest to northeast. Temperatures 25 to 31, upper 20s inside the Beltway.

5 to 9 p.m.: Snow, heavy at times, changing to sleet and freezing rain from southeast to northwest. Temperatures rising 27 to 34, near freezing inside the Beltway. Winds gusting up to 25 mph.

9 p.m. Sunday to 1 a.m. Monday: Sleet and freezing rain changing to rain from southeast to northwest. Temperatures rising to 32 to 45, mid- to upper 30s inside the Beltway. Winds gusting to 30-40 mph.

1 to 5 a.m.: Rain tapers off as dry slot comes through area. Temperatures: 32 to 41, probably mid-30s inside the Beltway. Winds gusting up to 25-35 mph.

5 a.m. to 9 a.m.: Variably cloudy, scattered rain and snow showers possible, no accumulation expected. Temperatures: 32 to 38, mid-30s inside the Beltway. Winds gusting to 20-30 mph.

9 a.m. to 1 p.m.: Becoming partly sunny. Temperatures: 35 to 41, upper 30s to near 40 inside the Beltway. Winds gusting to 25-35 mph.

What we’re reasonably confident about …

1. A strong winter storm will track through the region, passing west of the Chesapeake Bay

2. The storm will be strengthening as it tracks north and will produce a period of heavy precipitation across the area starting as snow Sunday afternoon into the evening, changing to ice and then rain across most of the area Sunday night, exiting early Monday morning

3. The track and strength of the storm will facilitate the development of strong winds from the east about 5,000 feet high.

4. Those easterly winds will help bring in an elevated warm layer off the Atlantic Ocean changing snow to ice and rain from southeast to northwest except for the very far western parts of the region into the mountains.

5. Temperatures near the ground will be slower to rise, especially as you get farther away from the Chesapeake Bay, especially toward Loudoun and Frederick counties.

6. Snow and ice accumulations will be lower the farther south and east you get from the city. Points northwest and west of the city will see the most snow and longest period of frozen precipitation.

We’re less certain about …

1. Exactly when the snow will arrive Sunday afternoon. The quicker it arrives, the greater the chance amounts could exceed our forecast. The later it arrives the more likely totals end up on the low end of our projections.

2. The exact track of the storm. The closer the storm tracks to the bay, the longer the low-level cold air and icy conditions will hold on.

3. How long freezing temperatures will hang in across the area Sunday night. We may need to wait for high-resolution model data over the weekend to refine our forecasts for the amount and duration of freezing rain. The higher resolution models usually do a better job simulating the persistence of low-level cold air than models now available.