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(CWG)
One of the biggest winter storms of the season so far seems to clutter up the accumulated snow region Wednesday and then curl on an ice storm. The heaviest snowfall and most icing probably occurs in the colder regions north and west of the city, but, with the exception of our more temperate southeast, much of the area is exposed to a violent winter storm.
The National Meteorological Service has published a winter storm watch because of the risk of significant snow and ice, which should lead to "very difficult" travel conditions on Wednesday.
The snow is expected to start before dawn on Wednesday and we anticipate the worst conditions will occur in the morning when widespread school closures and air travel delays are likely. Commuters on Wednesday morning may experience snow-covered and dangerous roads and reduced visibility when they decide to go out.
This will likely be the storm with the biggest impact since the January 12-13 snowstorm, which dumped about 6 to 12 inches of snow into the area. But this storm occurred during a weekend, and it will coincide with a busier mid-week travel and commute.
The storm will have two phases: a slippery and snowy phase Wednesday morning, and then, along and west of Interstate 95, an icy and sloppy phase that will continue in the afternoon and evening.
Snowfall is most likely to occur between Wednesday before dawn and noon, with ice and rain in the afternoons and evenings. Between these two phases, there will be a transition period during which the snow will turn into melted snow and freezing rain from south to north.
The heaviest snowfall of three to seven inches is expected in our northern regions, which will take longer to make the transition to ice and have the lowest temperatures. In the immediate metropolitan area, two to five inches of snow are most likely.
However, we can not rule out higher localized amounts ranging from about 4 to 8 inches, depending on whether and where small areas of heavy snow develop. Some models suggest that an area of strong snow could be established just southwest of Washington.
Southeast from Washington to southern Maryland, the snow will be brief, while near-freezing temperatures will limit build-up to about one to three inches.
Once the snow is over, melting snow and freezing rain become the dominant types of precipitation along Interstate 95 and west of Interstate 95 (Zones 1 and 2). Expect snow and melted snow to turn into solid rain in our southern and eastern regions, near Chesapeake Bay, and in southern Maryland (Zone 3).
Ice accumulation expected for Wednesday, February 20th.
One of the concerns about freezing rain is that it freezes the trees and can cause power outages if its weight starts breaking branches. It's a risk later Wednesday, especially when you factor in the extra weight of the previous snowfall. The threat will be highest in our coldest areas west and north of the Beltway (Zone 1). Temperatures in this area may remain equal to or below freezing throughout the duration of the event, which should lessen the night on Wednesday.
We expect closures and delays late Thursday morning due to rainfall until Wednesday night, especially in zones 1 and 2.
The above projections and the storm chronology, presented below, may be subject to adjustment in future updates, as the storm is still more than one day old.
Chronology of the Wednesday storm
NAM model of precipitation forecast during Wednesday's storm. The snow is blue, the rain is green, the snow is purple and the freezing rain is red.
4h to 8h: Snow developing from southwest to northeast. This could start as slush or a melted snow mixture, but it should go to the snow. Temperatures 28 to 34, from north-west to south-east. Accumulation of a coating to about one inch.
8am to noon: Snow, possibly heavy at times. Could mix with or change slush south of Washington in the late morning. Temperatures 27 to 32, from north-west to south-east. Accumulation of a few centimeters more.
From noon to 4 pm: The snow turns into slush everywhere, except for rain in the eastern and southeastern regions. Temperatures 29 to 34 northwest to southeast. Up to an inch or two more accumulation of snow and slush, the highest amounts north of Washington.
16h to 20h: Melted snow turns to freezing rain along and west of Interstate 95 (Zones 1 and 2) with cold rains elsewhere. Temperatures 30 to 35 northwest to southeast. Light glaze of ice possible.
20h Thursday at midnight: Freezing rain in the colder areas well north and west of Washington (zone 1), with rain elsewhere. Temperatures 31 to 35 northwest to southeast. Ice layer accumulated in the coldest areas (zone 1).
Thursday from midnight to 4 am: Rainfall is decreasing. Temperatures 31 to 36 northwest to southeast.
Impact of the storm
On the meteorological capital scale of impact of winter storms, this is an "upset" category 2 high-end storm in the immediate metropolitan area (Zone 2), but a "significant" Category 3 storm in our areas colder to the north and west.
In practical terms, we do not expect much difference in effect in these two areas during Wednesday's day. Both will face widespread accumulation of snow and ice, and slippery roads. But in Zone 1, the amounts of freezing precipitation will be a little higher and the water table conditions will last longer until Wednesday night and at night.
(CWG)
In our milder areas to the east and southeast of the city (zone 3), expect one to three inches of snow or less, this is more of a category "nuisance" storm 1, in which the effect of snow and ice will be more fragmented and shorter. lived – with probably just a brief period of tough conditions on Wednesday morning.
Why do we expect less snow than the National Weather Service?
By Wednesday morning, the The National Weather Service forecast 6 to 8 inches of snow in the Washington area. We think that it is too high by an average factor of two.
"I am not a proponent of forecasting large amounts of snow in cases where a low pressure zone was moving north and west, drawing in the north," said Wes Junker, expert on winter weather. at Capital Weather Gang. "The forecast of heavy snow could collapse if the heavy rainfall axis rises north of Washington and the warm layer arrives earlier than expected. I do not remember Washington having more than four or five inches of this type of event. "
However, Junker said the weather forecast could be verified in a boom scenario in which a strong localized snow band develops and / or precipitation takes longer than expected to move from snow to slush .
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