A winter storm will cause gusts of snow for Wednesday morning trips, then an ice-cold mix and rain

21:30. – The snow on the track must arrive before dawn; slightly lower accumulation prospects

Most of the late-afternoon and evening models have been reviewed and forecasts are generally in line with expectations. However, due to the dry air in the area, the snow can take an hour or two later to develop than expected – from about 6 hours, instead of 4 or 5 hours. This reduces the period of snowfall since moving to a winter area. the mixture is always expected between noon and mid-morning.

In response to reduced snow duration, the models reduced their snowfall forecasts in the immediate area to about 2 to 3 inches. Here are the latest figures of the afternoon and evening models for Washington:

• NAM: 2 inches
• SREF (average): 2.1 inches
• HRRR: 2.3 inches
• NAM high resolution: 3 inches
• European: 3 inches

Given the downward trend of the model's predictions, we are also reducing our prediction of 2 to 5-inch snowfall accumulation around Washington at 2 to 4 inches and 3 to 7 inches in our northern regions. and west at 3 to 6 inches.

Despite the high lower expected amounts, we are still expecting an accumulation of snow, perhaps strong, during the morning commute period followed by a messy winter mix. This will lead to difficult travel conditions. Our ideas and schedule described in detail below have not changed significantly.

This is our last update of the evening. We will resume coverage around 4 am Wednesday.

18h – Forecasts remain in line with expectations, with models suggesting a lower likelihood of a snow boom scenario

Since the initial publication of this article, a handful of additional model simulations have been made and support the ideas presented below. They all expect about 2 to 4 inches of snow in the immediate area in the morning, followed by a winter mix. However, these numbers are a little lower than some forecasts made Monday or even earlier today. For example, here are the latest snow model forecasts compared to the same forecast made 24 hours earlier, in parentheses:

• NAM: 2.3 inches (3.4 inches)
• High resolution NAM: 3.8 inches (3.5 inches)
• GFS: 3.0 inches (6.5 inches)
• SREF (average): 1.8 inches (3.6 inches)

We believe that the probability of a "prosperity scenario" of more than 5 inches has decreased in the immediate area. That said, we are still expecting snow on Wednesday's trips, which will create difficult travel conditions, followed by a jumble of mixed precipitation.

Original post of the afternoon

For the second time this year alone, a winter storm warning covers much of the Washington area this Wednesday, due to the risk of a dangerous combination of snow and ice.

We are especially concerned about Wednesday morning trips. The snow should move just before dawn and could quickly become quite heavy, which would limit visibility and make the roads dangerous at the heart of the normal traveling period.

Until Wednesday noon, the snow could accumulate quickly (about an inch per hour) and we expect widespread school closures. Airports are also likely to face delays and canceled flights.

We encourage telecommuting instead of commuting Wednesday morning to avoid important backups and to give crews the opportunity to operate. If you decide to drive, expect "very difficult" conditions, according to the National Meteorological Service.

The snow period (without precipitation mix) may not last very long, as the models suggest that precipitation will become slush, then freezing rain from mid-morning to mid-afternoon. south to north. The relatively fast passage should limit snow accumulations to about 2 to 5 inches in the immediate vicinity, with a little further north and west and a little less to the south and east.

If the transition to icy precipitation is delayed, the snowfall may exceed our expectations. But if the transition occurs on the fast side, we could see more quantities in the range of 1 to 3 inches.

Another area to watch for during this storm is a possible localized area of ​​heavy snowfall. The models vary as to exactly where it will occur, but we can not exclude some totals greater than six inches. The general trend would be to support jackpot amounts in our coldest areas located to the west and northwest of the city, but they can not be excluded in the immediate metropolitan area.

Even after the passage of snow-ice precipitation, the threat of dangerous conditions is far from over, especially in our colder regions. Visibility tends to improve when the snow turns to slush and melted snow does not accumulate as fast as the snow, but untreated pavements and sidewalks will remain slippery even into the snow. 39, afternoon. The exception may be in our milder areas to the south and east of Washington, where temperatures rise above zero and precipitation turns into ordinary rain.

Later in the afternoon and evening Wednesday, along and west of Interstate 95 (zones 1 and 2 of the map above), the sleet will move to a new Freezing Rain. Freezing rain forms an icy glaze on contact with cold surfaces. In addition to creating untreated smooth surfaces, it can accumulate on distribution lines and break tree branches, resulting in power outages.

Our most northerly and westerly zones (Zone 1) present the highest risk of significant ice accumulation of at least a slight glacis (or 0.1 inch), sufficient to cause tree damage and power outages. In these areas, temperatures will remain near or slightly below freezing point until Wednesday evening or Thursday morning in the coldest places (northwestern Virginia and northern Maryland). Near Interstate 95, we expect temperatures to rise slightly above the freezing point by Wednesday night. Average freezing rain would change to ordinary rain before larger ice accumulation.

We expect rain and freezing rain to end everywhere before dawn on Thursday, but some school delays and closures are likely on Thursday morning due to earlier precipitation. Some untreated roads, car parks and sidewalks are likely to remain slippery on Thursday.

Detailed chronology of the storm

3h to 6h: 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.

6h to 10h: Snow, possibly heavy at times. Could start mixing or turning into ice pellets south of Washington. Temperatures 27 to 32, from north-west to south-east. Accumulation 2 to 4 inches, less south.

10h to 14h: The snow is changing everywhere, except in case of rain in the very south and south-east regions. Rainfall decreases some in intensity. Temperatures 28 to 33 northwest to southeast. Up to an inch or two more accumulation of snow and slush, the highest amounts north of Washington.

14h to 18h: 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. A light layer of ice is possible in the coldest areas.

18h Thursday at midnight: Freezing rain in the colder areas well to the north and west of Washington (Zone 1), freezing rain changing to rain near Interstate 95 (Zone 2). Rain elsewhere. Temperatures 31 to 36 northwest to southeast. Ice layer accumulated in the coldest areas (zone 1).

Thursday from midnight to 4 am: Rainfall is decreasing. Temperatures 32 to 37 northwest to southeast.

Models

Here's how much snow the different models predict around Washington:

• SREF (average of 24 simulations): 1.8 inches (range: trace up to 4.5 inches)
• NAM: 2.3 inches
• GFS: 3 inches
• European: 3 inches
• High resolution NAM model: 3.8 inches
• HRRR: 3.8 inches
• Canadian: 4.8 inches
• High resolution Canadian: 7.2 inches

Note that some of these model predictions consider slush as slush while slush tends to actually limit snow accumulation.

"The big question mark is whether the heavier snow band touches us and ends up in northern Pennsylvania, like the high-resolution NAM model and, to a lesser extent, the European model, or falls down. about us, as Canadian models predict, "says Wes Junker, Capital City's winter weather expert.

"In the first scenario with less snow, precipitation is concentrated along a frontal frontier that forms northward between the warm air that rises to the north in Kentucky and the west. West Virginia, "said Junker. "It often happens with these types of systems. We have a few hours with a snowfall that turns into slush, then a lighter freezing rain and possibly rain. "

"This last evolution, which would bring more snow, is rarer but can not be totally ignored and seems to me to be the most unlikely scenario of both. This would be a boom scenario that is always possible and helps to explain why there is still so much disparity between snow forecasts from different outlets. "

Forecast of other points of sale

National Meteorological Service

NBC4

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.