This story will be updated through the evening commute.

A winter weather advisory is in effect until 7 p.m. for the entire D.C. metro, northern suburbs and Baltimore. It does not include Charles, Calvert or St. Mary’s counties.

12:50 p.m. update: We’re watching temperatures carefully as precipitation inches toward the Beltway. North and northwest suburbs are still below freezing, and will probably remain that way though most of the afternoon now that sleet is falling. Temperatures are up to 33-36 degrees in the Beltway, which will initially preclude icy accumulation, but it will get colder as the rain and/or sleet falls.


Temperatures at 12:50 p.m. (Weather Underground)

12:00 p.m. update: Sleet is falling in the far northern suburbs, including Frederick, Gaithersburg, Germantown and Leesburg. Sleet and freezing rain is moving into the Baltimore area from west to east, coating the untreated surfaces with ice. As the hours pass, the rain and sleet will creep farther south toward the Beltway. Temperatures could drop, making it more likely for ice to develop on untreated roads.

The Monday evening rush could be hazardous as a wintry mix skirts through the D.C. region just as commuters head out the door, especially in the northern suburbs.

Snow is not really going to be the issue tonight — the concern will be the chance of icy roads due to sleet and freezing rain. Temperatures seem likely to rise above the freezing mark this afternoon, which would preclude icy accumulation. However, as the precipitation falls, it will cool the air, which could drag the temperature back down below freezing. That in combination with very cold roads (thanks to the recent prolonged cold snap) suggests untreated surfaces could become slick.

In many ways, this so-called wintry mix can be more dangerous than snow. Be prepared for icy roads — particularly side streets — and sidewalks. Allow extra time for the commute.

Timing: Monday from 3 p.m. to 7 p.m.

Hazard: Light freezing rain, sleet and snow

Impacts: Icy glaze on untreated surfaces, including roads, sidewalks, driveways and parking lots

Confidence: Medium

Forecast details

The main uncertainty in this forecast is the temperature. If it stays above freezing through the duration of the event, there will not be hazardous accumulation. If it drops below freezing then ice could start to develop on the roads. The forecast is right around 32 degrees, so it could go either way.

These are a few reasons we are concerned about ice this evening:

1) The air will initially be dry. So any rain falling through it will evaporate, which will cool the air. Even if the temperature gets up above freezing this afternoon, it could drop rapidly once the precipitation arrives.

2) Arctic air often holds on a little longer than forecast, and we are only just coming out of a prolonged cold snap. In these situations, the coldest model forecast usually ends up being closest to reality unless strong surface winds are present. The high-resolution NAM model suggests, despite the lack of a high pressure system to our north to promote cold air damming, temperatures will stay at or below freezing for most areas north and west of the city.


NAM temperature forecast for 4 p.m.

The NAM also indicates temperatures will fall back to freezing even around the Capital Beltway once the precipitation starts. The NAM is predicting below-freezing temperatures as far south as the District. By 7 p.m., the model drops the temperature to 33 degrees as far south as Waldorf and Dale City.

Other models forecasts are a little bit warmer — notably the GFS, which keeps the District at 35 degrees at 4 p.m. With light winds being forecast, it is hard to rule out the NAM’s colder, icier prediction.

3) The ground and untreated surfaces are likely to remain well below freezing because of the extreme cold of the past couple of weeks. If that is the case, rain would freeze on contact, even if the air is warmer than 32 degrees. For that reason, even folks living in areas where the temperature rises a little above freezing south and east of the city should not let down their guard and should monitor road conditions.

The precipitation should clear out from west to east but could linger across our eastern areas into the evening hours. Precipitation will be over well before tomorrow morning, but temperatures will drop below freezing again tonight, which raises the potential for icy patches in the morning commute.

The Capital Weather Gang takes us through their predictions for the upcoming 2017-2018 winter weather in Washington, D.C. (Joyce Koh/The Washington Post)