DMV winter storm: Snow, ice expected to slam region on Sunday before bitter cold workweek

WASHINGTON - Over the last 24 hours, weather models have finally come into general agreement on how this storm will play out for the D.C. region this upcoming weekend. 

Light snow starts late Saturday night into just beyond the midnight hour Sunday, it picks up in intensity overnight region wise and is heaviest during the early morning hours, before it transitions to a period of sleet and perhaps freezing rain (icing) in the afternoon. The system then exits the D.C. region late Sunday night.

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Icy impacts:

One thing that may be a surprise is the air temperature throughout the course of the event. 

Most of the region will stay in the teens and peak only in the middle-to-upper 20s throughout the entire event. With temperatures like that you would think that you might be looking at just all snow, but about 5000–7000 feet in the air say otherwise. 

A strong jet of air above freezing will push northward in this layer, melting snow as it falls through it and causing it to fall as sleet, and in areas where it is pronounced enough, freezing rain.

As mentioned above, timing the shift and how far north this warm layer comes will be the most difficult part of the forecast over the next day ahead of the storm starting here in Washington, D.C. 

How intense the warm layer is also plays a role on whether it is sleet (ice pellets) or freezing rain (falls like rain but freezes on contact).

Examining a lot of the evening guidance, a lot of them suggest a rather soft warm layer initially around and north of D.C., that intensifies as the afternoon goes on. 

Thus, I am of the opinion that we are likely looking at a more prolonged period of sleet than freezing rain. This said, I do still expect some freezing rain to work its way in, likely later in the afternoon or early evening hours of Sunday when the warm layer is at its strongest.

Between 0.1" to 0.2" of ice seems possible on exposed surfaces. South and southeast of town, they are more likely to see more prolonged freezing rain and over a quarter inch of ice seems possible in these locations. 

The fact that most of these surfaces will be snow covered will help mitigate some impacts, but the liquid rain will compact snowfall and seem below the snow layer before freezing in many cases, so expect it to harden the snowpack and put a light layer of ice on solid surfaces.

Weaker winter tree branches and powerlines already dealing with the extra weight of a snowfall could limp or break with the additional weight of ice, especially in our southern zones where the icing threat is greatest. 

One thing that should help limit power outages to a degree is this storm system is not coming with any sort of strong or prolonged winds that would exacerbate these impacts, but there will still likely be a few outages, most likely Sunday evening.

Winter's fury:

With so much focus on the snow, many people haven't realized what is coming right after the main event, that will prolong cleanup efforts in the D.C. region: Cold. Extreme cold.

January is D.C.’s coldest month. We are no strangers to cold air outbreaks this time of year. Only four times in D.C. history has the city failed to get above freezing for nine days in a row or longer, the most recent of which was 10 days back in December 1989. 

At the moment, starting tomorrow, most weather models suggest we will do just that. This includes several nights at or below record low temperatures in the single digits. Cold of this magnitude for such a prolonged period of time will not only hamper cleanup efforts from this storm, and likely prolong school and office closures well into next week, but also lead to additional issues with things like water main breakdowns.

Next week’s dangerous cold is a major story. That will just be another piece in what has already been a very memorable winter temperature wise. 

Some weather models have even hinted at the potential for more snow around next weekend, but they continue to go back and forth with that possibility, and it is far too early to give the threat any credibility. Though we will continue to monitor for the threat for any additional snowfall as we get into next week.

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