Snow, sleet threaten DC region Wednesday morning

A system that we have been keeping a close eye on since last week now appears likely to bring impactful winter weather to the Washington, D.C. region on Wednesday morning. Currently, significant impacts to travel are expected as conditions worsen through the morning hours. Widespread school and likely some government delays and cancellations are anticipated due to the timing of this storm.

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On Monday morning the National Weather Service out in Sterling, Virginia issued a Winter Storm Watch for much of Maryland, Virginia, parts of West Virginia, and the District of Columbia. In the watch advisory, National Weather Service noted that "the potential exists for five or more inches of snow" for those who are under this watch zone. In addition, they are concerned with the potential for accumulating ice as the storm system transitions from a snow to a mix to a freezing rain event throughout the course of Wednesday. Similar to the event that hit the region early last week, some untreated surfaces and trees could become ice covered and some down trees and power outages cannot be ruled out as a result. The areas at greatest threat for freezing rain and ice with this storm look to be north and west of town.

As for timing, current weather model guidance suggests that the snow initially begins to develop in far southwestern Virginia in the 12 a.m. hour early Wednesday morning, growing and advancing to the northeast through the pre-dawn hours. Snow is currently expected to reach the immediate Washington, D.C. metro region between 3 a.m. and 7 a.m. Wednesday morning. The snow could rapidly pick up in intensity, with the potential for half-an-inch to one-inch per hour snowfall rates. This is enough to reduce visibility and coat even treated roadways in a layer of slippery snow and slush.

As the storm continues to progress, warmer air will eventually start to win the day in the middle layer of the atmosphere. This will start to transition the snow over to sleet, and then eventually freezing rain. The changeover will occur fastest in our southwest zones. Southern Maryland, the lower Eastern Shore, and the Northern Neck should all start the transition process by the middle to late morning hours. The farther north and west you go from there, the longer the wintry precipitation will try to hold on.

Here in Washington, D.C., the transition from snow over to sleet and freezing rain is most likely after the 1 p.m. hour. One question we still have is when does the change to plain old rain occur, instead of the mixture of sleet and ice. Weather models continue to debate this, with some model suggesting this may not until the evening hours here in the city, and may even linger into the overnight hours in some of the zones north and west of town.

One thing that we do have to watch for when these types of events is that models tend to overestimate how quickly we transition to all rain here in parts of our region, particularly north and west of the metro area. Many times cold, subfreezing air gets trapped at the surface and sleet and freezing rain are able to linger well beyond when weather models say they will. This means impacts could potentially linger into the early morning hours of Thursday as far as ice is concerned in some of those northwest zones. So the potential for school delays and closing does exist as well, depending on just how much snow falls in these zones, and how much sleet and ice they pick up after the transition.

It's also important to note that at this time, we do not have a single weather model saying that our region will get no snow at all. Most are going between two-inches to seven-inches for the District of Columbia, with more expected to the west and less to the east. The tricky part of this system will be all about the transition from snow, to sleet, to rain. Nailing down an exact time for when that transition occurs is what will cause snowfall numbers to likely need some adjustment the 36 hours.

Stay tuned, and the Fox 5 Weather Team will continue to keep you up to date on all the latest changes as we track the midweek winter storm.

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