This article has been updated to include Capital Weather Gang’s accumulation forecast map.

Sunday evening update, 9:40 p.m.

After reviewing the afternoon and evening models, we see little need to change the forecast for the event late Monday through early Tuesday. The precipitation may start a bit later in the afternoon (than indicated below) when temperatures will have risen well into the 30s to near 40, which is likely to mean it starts as rain. However, models continue to show rain changing to a wintry mix during the evening which is when we anticipate the possibility of some slick roads and reduced visibility, especially north and west of the city.

Original article from the afternoon

Computer models have trended slightly colder for the winter weather event predicted in the Washington region on Monday afternoon and night, increasing the likelihood of slick travel. Meanwhile, a second potential winter storm Wednesday night into Thursday bears watching but may just end up skirting the area.

The storm late Monday promises to bring a wintry mix to the region, with the greatest amounts of frozen precipitation and threat of slick roads north and west of downtown Washington. However, should heavy bursts of precipitation develop Monday evening, much of the area, with the exception of Southern Maryland, could see some slipperiness and a light accumulation of frozen precipitation.

While amounts are highly uncertain, a coating or so of frozen precipitation is most likely in the immediate area, with up to one to three inches of snow and sleet north of Leesburg, Rockville and Baltimore. However, such amounts cannot be ruled out even into the immediate Washington region if there is a heavy burst of snow and sleet Monday evening as some modeling suggests (boom scenario).

In addition to any snow and sleet, a light glaze of freezing rain is possible north and west of downtown Washington.

The period of greatest concern is between about 4 p.m. Monday and predawn Tuesday, and it includes the Monday afternoon-evening commute. Light precipitation could linger into early Tuesday morning, with temperatures hovering near freezing in our colder areas but probably rising a little above freezing elsewhere. Our colder areas could experience iciness on roads and walkways into early Tuesday morning before temperatures rise above freezing by mid- to late morning.

A more significant coating of ice, capable of producing tree damage and power outages, is possible toward the Interstate 81 corridor, which is under a winter storm watch.

Monday-Tuesday storm timeline

1 p.m. to 5 p.m. Monday: Precipitation begins from southwest to northeast. It may begin briefly as rain before changing to snow and sleet. In our southern and eastern areas, it may remain rain. Temperatures in the mid- to upper 30s in the early afternoon fall to the low to mid-30s.

5 p.m. to 10 p.m. Monday: Sleet and/or snow around Washington and especially points west and north. Some accumulation possible (snow accumulation highest north of Leesburg, Rockville and Baltimore). More rain or rain and sleet to the south. Temperatures close to freezing in the immediate Washington area, slightly below freezing north and west of the Beltway, and a little above freezing to the south and east.

10 p.m. Monday to 3 a.m. Tuesday: Sleet and/or snow changes to freezing rain north and west of downtown Washington with temperatures near freezing. Mostly rain elsewhere with temperatures a little above freezing.

3 a.m. to noon Tuesday: Freezing rain/drizzle may linger in our colder areas north and west of the Beltway before changing to patchy drizzle after sunrise and then ending. Temperatures rise from the low 30s to the mid-30s. Elsewhere, patchy light rain and drizzle gradually taper off, with temperatures rising into the mid- to upper 30s.

Complications in the forecast Monday and Monday night

Knowing exactly what types of frozen precipitation fall, and when and where, is complicated. Computer models differ on where the dividing lines for snow, sleet, freezing rain and rain will set up.

As precipitation begins late Monday afternoon, temperatures will drop toward freezing in the immediate area and just below freezing to the north and west. That probably will result in a mix of snow and sleet for the immediate D.C. area and northward, at least initially.

How much the snow might accumulate will depend on the intensity of precipitation and what percentage falls as snow vs. sleet. Around Washington, the temperatures aloft are predicted to have a rather deep layer right around freezing. That would support snow but warm any part of that layer to a little more than a degree above freezing, and the precipitation would fall as sleet, which would keep accumulations down but still could leave an icy coating on the roads, at least for a time.

As Monday night wears on, a warm layer will develop and snow and sleet will change to freezing rain west and north of the city and plain rain to the south and east.

Heavier precipitation and temperatures on the cold side of forecasts will mean more snow and ice, extending farther south. But if precipitation is light and temperatures are on the warm side of forecasts, this will be mostly a rain event, with icing reserved for mostly our outlying colder areas to the north and west.

Storm chance Wednesday night and Thursday

The chance of a major snowstorm Wednesday night into Thursday is in doubt, but light snow could fall even if there are not significant amounts.

Shifting away from its forecast for a big snow event, the American (GFS) model has joined the European model in forecasting only light amounts of snow.

The Canadian model still predicts light to moderate snow in the region, but it has decreased its predicted amounts compared with its forecasts on Saturday.

With the storm 3½ days away, it’s not out of the question that models trend back to the north, increasing the chance of significant snowfall. For now, this is how much the different models project for Washington:

  • American: 0.8 inches
  • Canadian: 3.4 inches
  • European: 0.8 inches
  • UKMet: 0 inches

The bottom line is that the chances of a significant storm have diminished but the event warrants monitoring closely.