* Winter weather forecast 10 am Thursday at 10 am Friday *
A rather modest weather system will invade the Washington area from Thursday to Friday morning. But there can be just enough moisture and cold air for snow accumulation, especially in the cold regions north and west of the city.
This snow could lead to travel delays and school disturbances on Friday morning.
A few inches of snow, possibly mixed with slush, is possible just north of downtown Washington, including Vienna, Bethesda, Olney and Columbia. Projected quantities will reach about one to three inches in northern Maryland and northwestern Virginia.
In both northern areas, untreated roads and sidewalks could become slippery, especially during moderate to heavy snowfalls.
From downtown Washington and south, a mix of snow, slush and rain is likely. Here, most snowfall, if it materializes, would most likely be limited to grassy areas, mulch and car roofs, as the air and cladding temperature will likely remain close to freezing or overheating. above zero. That said, if a thick snow or slush band develops over this area, we can not exclude a period of slippery roads and reduced visibility.
"The greatest threat of impact of this snowfall during the Friday morning rush hour will be north of the Interstate 495 Capital Beltway," said the National Weather Service. written in a special statement, and we agree. "If you plan to commute on Friday morning, be aware of the risk of disruption of your trips. Plan ahead by planning additional travel time and consider using public transit and telecommuting options. "
Chronology of the storm
10 am Thursday at 2 am on Friday: Snow is growing in our northern regions, with a winter mix developing elsewhere – from west to east. Temperatures 33 to 39, from north-west to south-east. Few problems expected.
Friday 2h to 6h: The heart of the event. Snow, probably moderate to strong in our northern regions. Snow and / or slush in our immediate vicinity. A winter mix of snow, slush and rain in our southern regions. Temperatures 30 to 34 degrees, from north-west to south-east. Slick spots possible mainly north and northwest of the Beltway.
Friday from 6h to 10h: Rainfall decreases gradually to create a drizzle from west to east. Temperatures 31 to 34 degrees, from north-west to south-east. Slick spots possible, mainly north and northwest of the Beltway.
Impacts of the storm
On the meteorological capital The winter storm impact scale is considered a Category 2 "disruptive" event in our northernmost regions, due to the combination of one to three inch snow, frost-like and lower temperatures, and falls. of snow affecting daily movements. Smooth spots and delays are likely.
In the area where we expect less than two inches of pavement, this event is considered a Category 1 "nuisance" event, which could result in slippery areas, but this should not cause any major problems unless surprised.
To the south, where we do not expect an accumulation of one inch, it is a category 1 at the limit of what is barely on our scale. Its impact will depend on the possibility that the snow is sufficiently stable so that the temperature of the air and the lowered ground reaches the freezing point and leads to slippery areas.
Model forecast and discussion
This forecast, like many snow events in the Washington area, is tricky because the model's predictions vary considerably. Here is the forecast gap in downtown Washington:
- NAM high resolution: 0 inches
- NAM: 0.1 inches
- HRRR: 1.0 inches
- SREF: 1.1 inches
- Canadian: 1.3 inches
- GFS: 1.5 inches
- European: 1 to 2 inches
- HREF: 2 to 4 inches
- Canadian high resolution: 3.1 inches
Note that these models assume that each snowflake will stick, which is a bad assumption for this event as temperatures, especially outside our coldest areas to the north and west of Washington, will be above the freezing point during part of the event.
"There are two related issues that make this prediction difficult," said Wes Junker, Winter Weather Expert at Capital Weather Gang. "Where will the highest precipitation band go and how fast will surface temperatures fall below freezing?"
He continued, "If the band goes north of us, as predicted by the NAM models, the city could receive only a layer of snow or even a lot of slush, because the precipitation would not be sufficiently cooled down. to eliminate a warm layer at mid-height. In addition, surface temperatures may have difficulty falling to frost.
"But if you increase the more abundant precipitation towards the south, the temperatures in the immediate area will be colder and it could be that the falling night is mainly covered with snow with a potential of a few centimeters.
"A slight change from the precipitation axis could make all the difference between the lack of snow accumulation and the difficult morning commutes in and around the city."