A mix of snow, ice and rain is expected in the Washington region Saturday, but it is more likely to be a minor inconvenience than particularly disruptive. The exception may be in the far northern and western suburbs, where frozen precipitation may be a little heavier and last longer than elsewhere.
Computer model forecasts have trended away from a meaningful winter weather event in most of the area by delaying the onset of steady frozen precipitation. We will still have a high-pressure zone to the north feeding in cold air early Saturday morning. However, the timing of the onset of precipitation has slowed, and steady precipitation is initially aimed well north and west of Washington into Pennsylvania and West Virginia.
Frozen precipitation during the early- to mid-morning hours in the immediate D.C. area and points east should be light and patchy.
There is still potential for a brief period of steadier snow and sleet in the morning hours, mainly in our northern and western areas, and then a longer period of light freezing rain that could hang on into the afternoon. However, the onset of steady, heavier precipitation is delayed long enough for the city and south and east to escape with patchy light snow, sleet and freezing rain before a fairly quick changeover to rain during the afternoon, if not earlier.
In general, because the storm system is expected to pass so far north and west of Washington, precipitation amounts are forecast to be light.
The National Weather Service has come up with a pretty reasonable first projection of snowfall totals, which shows the best chance for more than a coating in northern Maryland, from Frederick north. These areas could also see a period of sleet and freezing rain during the afternoon before precipitation ends.
This weather system should move through pretty quickly, with precipitation ending in the region between 4 p.m. and 7 p.m., from southwest to northeast. By this time, most areas should have risen above freezing as a result of winds from the south ahead of the storm system (passing to the north).
The period of greatest concern for slick travel is between midmorning and early afternoon, when steadier precipitation develops.
As the event is still three days away, there is uncertainty and the possibility that this event could be more disruptive if the steadier precipitation streaks into the area earlier when temperatures are still low enough for widespread snow accumulation.
We present a couple of scenarios below but lean toward Scenario 1, based on how forecasts have trended over the past day.
Scenario 1: Little impact from the city south and east. Some slick travel possible north and west (70 percent chance).
The most probable scenario is for light snow and/or sleet to spread across western parts of the region Saturday morning before transitioning to brief freezing rain and then rain during the afternoon.
The initial push of accumulating frozen precipitation would mostly miss the immediate area and south and east, passing to the west and north, while patchy light snow and/or sleet would be possible. This would probably allow temperatures to rise above freezing before significant precipitation affects the area. Slick spots, if any, would be limited and short-lived. In far south and east areas, toward Southern Maryland, mostly rain would fall.
In this scenario, the biggest risk of accumulation of snow and ice would be north and west of the Beltway and would probably be limited to a coating to an inch, except a little more in northern Maryland. Untreated paved surfaces could turn slick for a time Saturday morning, but conditions would improve in the afternoon as the temperature rises above freezing.
Scenario 2: Some slick spots possible in most areas, with greater impacts north and west (30 percent chance).
In this scenario, the steady frozen precipitation overspreads the area a little more quickly, and the cold air hangs around longer, especially north and west of the city.
The city and nearby suburbs would still probably see only a dusting to an inch of snow and mixed precipitation, but temperatures could stay low enough for a thin coating to develop on roads leading to slick spots through the morning hours, perhaps into early afternoon. In our colder areas far to the north and west, temperatures could remain near freezing for most of the event, with snow and ice totals of up to 1 to 2 inches.
Even in this scenario, areas well south and east of Washington, toward Southern Maryland, would see mostly rain after perhaps a brief period of light snow and/or sleet.
We’ll try to pin down the forecast in greater detail in our update Thursday.