Canadian model forecast at 7 a.m. Tuesday.

After a mild week of highs in the 50, 60s and 70s, a much colder weather regime barges into the region this weekend. This sets the stage for a long-duration wintry precipitation event Sunday evening through Tuesday — when we can expect an intermittent mix of snow, sleet, freezing rain and/or rain.

Right now, this doesn’t have the look of a major winter storm but, rather, a drawn-out nuisance that could bring intervals of slippery travel — especially in our colder areas to the north and west of downtown Washington.

While cold air will be in place, it does not appear as though it will be deep enough to support a significant snowstorm. The layer of cold air is likely to be shallow or close to the ground — favoring more of a mix of precipitation. The chance of seeing an inch of snow is in the 20 to 30 percent range (the higher end of this range applies to our colder north and west areas).

Temperatures throughout this period will hover close to freezing or a little above, meaning it will likely just be marginally cold enough for iciness. Based on current information, the problem areas — where it could turn slick at times — would tend to focus in our colder areas north and west of the Beltway. Vulnerable to turning icy? Untreated sidewalks, side roads, driveways and parking lots and elevated surfaces like bridges, ramps and overpasses.

Here’s a rough guide of what to expect and when, subject to adjustments, based on the latest model forecasts ...

Sunday evening into early Monday morning: Starting between 7 p.m. and midnight, light mixed precipitation is likely. Snow could mix with sleet and freezing rain, especially north and west of downtown. A slick coating on untreated surfaces cannot be ruled out. From downtown and to the south and east, more rain and sleet are likely — with mostly wet conditions.


NAM model shows light freezing rain over the area Sunday evening. (PivotalWeather.com/PivotalWeather.com)

Monday during the day: The precipitation should ease, with some lingering drizzle, or even stop. Temperatures rise above freezing, to 35 to 40 degrees.

Monday evening into early Tuesday morning: Precipitation redevelops and temperatures fall back toward freezing. North and west of downtown, mostly sleet and freezing rain are likely, although snow may be part of the mix initially. Conditions could turn slick again, especially on untreated surfaces. From downtown to the south and east, a wintry mix (of sleet/snow/freezing rain) is reasonably likely at first but should gradually transition toward plain rain.


European model shows freezing rain west of downtown Washington at 7 a.m. Tuesday morning. (WeatherBell.com)

Tuesday during the day through the evening: Freezing rain should slowly change to rain north and west of downtown, but may take into the afternoon in our colder areas. From downtown to the south and east, mostly plain rain should fall.

Forecast discussion

The above forecast is based on a blend of model predictions. The European and Canadian model forecasts are currently colder and icier than the American model, which projects less frozen precipitation and more rain (this is a change from yesterday, when the situation was the reverse).

The models differ because it is a complicated weather pattern with competing players.

“Two features, a strong surface high to our north and a low tracking to our north and west will be battling for supremacy,” said Wes Junker, Capital Weather Gang’s winter weather expert. “The high is likely to promote a feed of shallow cold air east of the mountains, but even then, the air mass is only marginally cold enough to support meaningful impact.

"The low to our north and west will be pumping a southerly stream of warm air toward us at the mid-levels of the atmosphere. That warm surge aloft argues against a prolonged period of snow but doesn’t completely rule out iciness in our typically colder locations north and west of the city. "

We lean toward the colder-model solutions, because the wedge of cold air from the high pressure zone is often difficult to dislodge.

That said, forecast specifics — including exact temperatures and precipitation type and timing — are likely to evolve some over the weekend, so check back for updates.