The Interstate 95 corridor has plenty of wild cards. More significant accumulations are possible in the northwest. Despite the buzz on social media, the rains won't start for another three days. A lot can change between now and then, which means it's important to check for updates often and not assume today's forecast is “locked in.”
The National Weather Service will begin drawing winter storm watches late Wednesday or early Thursday for areas with the highest potential for heavy snowfall. Most meteorologists can take a first stab at putting specific numbers on a map for projected snowfall, with some accuracy.
For now, let's look at what has changed since our previous predictive rating, review what we know and don't know about the system, and find reasonable expectations.
An upper-air disturbance swinging southeast over the lower 48 will meet with moisture in the southern Plains on Friday. As it progresses eastward, it will create a new low pressure area in the mid-Atlantic that will intensify as it rides northward off Virginia Beach. Precipitation will rise northward ahead of the system. Some will move back to the western side of the system, where northerly winds will pull colder Canadian air south to form snow.
The path and strength of the system remains questionable, which is why it's difficult to predict what kind and how much precipitation will fall east of the mountains.
What's New in Forecast
- Models continue to struggle with strength A storm develops in the mid-Atlantic and slides south of New England. The US GFS model has a slightly farther offshore and weaker low. The European model, meanwhile, depicts a close track of a strong low-pressure system, but close passages typically mean warmer air being pulled inland from the ocean and more rain than snow near I-95. However, a stronger storm system in that scenario could lead to more precipitation, which could help cool the lower atmosphere and increase snow in some areas.
- Both major weather models now agree on a sharp transition zone between rain and snow near Interstate 95 south of New York City from Washington. Along and east of I-95, more rain than snow is possible. Thirty to 60 miles to the northwest, the chance for significant snowfall increases.
- Models are converging on the idea of an early period of snow in parts of the Mid-Atlantic, mainly west of I-95, as the storm begins Saturday. It will only last for a few hours, but there may be enough snow to disrupt travel for a while. After that, precipitation may change to rain at lower elevations.
Time and possible totals
Heavy showers and thunderstorms will develop over the deep south and southeast on Friday night. As precipitation creeps into the northeast Carolinas and southwest Virginia, some freezing rain is possible over higher ground. Moisture will slide over the shallow lip of the frosty air, and the mountains will bleed.
By early Saturday morning, snow will fall across eastern West Virginia and much of central and West Virginia. Washington, Baltimore and Philadelphia will have snow showers for a few hours, perhaps briefly heavy, changing to snow and rain in the afternoon. However, it is not set in stone.
Snow then works its way into northeastern and southern New England overnight Saturday evening. New York City could see several inches of snow, but as the rain-snow line flirts with the city, the transition to snow and rain could limit its amount. Locally, more snow is expected. The National Weather Service, which serves New York City, expects heavy snow accumulation across the Lower Hudson Valley and southern Connecticut.
Midwestern Pennsylvania and the southern Hudson Valley will have a sharp westerly shear for snow. In southern New England, rain and snow will mix with snow inside Interstate 495, but snow is possible, especially northwest of Mass Pike and Interstate 84.
Boston and Providence could see several inches of snow before the rain moves in Sunday afternoon or evening, though the weather service office serving the region writes that “specifics are still fuzzy.” Providence may see less snow than Boston, especially if the European model showing a strong low is correct, and more moisture will be pulled toward the coast.
The storm center could be too far east for significant snowfall over much of New Hampshire, Vermont, and interior Maine; There is a strong chance of snow on Sunday along the Maine coast.
The “sweet spot” of moisture with cold air isn't very wide — 50 miles or so — but it's most likely on the eastern slopes of the Appalachians, where 6 to 10 inches of snow and the potential for snow are possible. High volume locally.
As the system moves quickly, rainfall amounts are not as large compared to other systems.
Washington will end up on the wetter side of the rain-snow line
All signs are flanked by the winter elements of the Washington system. As abundant precipitation falls (0.75 inches or less), temperatures will warm in the mid-levels as the storm moves through. That's why after Saturday morning to afternoon wet snow, drizzle and then rain will start to fall.
“The forecast for I-95 and points east is set for a mostly rainy event that will begin with little snow or accumulation,” said Wes Junger, winter meteorologist with the Capital Weather Gang. “The rain-snow line will be dictated by how far westward it moves and the intensity of precipitation west of urban accumulations. The highest probability of meaningful snow will be near and in the mountains.
It's not out of the question that Washington's western suburbs will see an inch or two of snow before the transition to snow and rain.
Instead of turning to rain Saturday afternoon, snow could continue into Saturday evening in the Potomac Highlands and areas northwest of Montgomery and Loudoun counties. This could be a storm in which Leesburg and, in particular, Winchester County will see significantly more snow than areas in a county periphery.
Precipitation will end in the Washington area before dawn on Sunday. The timing of the storm has been accelerated, which means hopes for a dry Sunday have increased, barring the chance of rain or snow showers.
There are some uncertainties – namely the specific path and strength of the low pressure system. It's probably best suited for Wednesday night or Thursday. A parent upper-air disturbance is moving ashore in the Pacific Northwest, meaning meteorologists can launch weather balloons into it. That big data model will enable more accurate forecasting and modeling.
It's also unclear how strong “50-50 less” would be. It is a low pressure system that will form near 50 degrees north latitude, 50 degrees west longitude – Canadian waters. It will swirl in cold air, but a major snowstorm won't be enough for much of the I-95 corridor.
Jason Samenow contributed to this report.
