What we know about a possible East Coast snowstorm this weekend

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By journalsofus.com


A storm is brewing on the East Coast this weekend. A drop of moisture will deliver moderate to heavy precipitation, some wet and some white. Major cities like Washington, Baltimore and Philadelphia will likely walk a tightrope between a flooded storm and plowable snow. Boston and New York City may be putting gas in the snowplows.

There are plenty of wild cards left for the Interstate 95 corridor. Further northwest, larger accumulations are likely. Despite rumors on social media, rainfall will not arrive for three days. A lot can change between now and then, which means it’s important to check for frequent updates and not consider today’s forecast as “fixed.”

The National Weather Service will likely begin issuing winter storm warnings late Wednesday or early Thursday for areas where the chance of heavy snowfall is highest. That’s the time when most meteorologists can, with some accuracy, first try to put specific numbers on a map for projected snowfall totals.

The DC area is usually near the rain-snow line. This is why.

For now, let’s review what has changed since our previous forecast assessment, review what we know and don’t know about the system, and identify reasonable expectations.

An upper-air disturbance moving southeast over the Lower 48 will encounter moisture over the southern Plains on Friday. As it moves eastward, it will generate a new area of ​​low pressure in the Mid-Atlantic that will intensify as it moves northward off the coast of Virginia. Precipitation will increase northward, ahead of the system. Some will return to the west side of the system, which is where northerly winds will push cold Canadian air south and produce snow.

The track and strength of the system remains questionable, making it difficult to say what type and how much precipitation will fall east of the mountains.

What’s new with the forecast?

  • The models continue to fight with strength. of the storm that will form in the Mid-Atlantic and slide south of New England. The US GFS model has a slightly further offshore and weaker low. Meanwhile, the European model represents a closer pass of a stronger low pressure system, but closer passes generally mean more warm air pulled inland from the ocean and more rain than snow near I-95. However, the stronger storm system in that scenario would bring heavier precipitation, which could help cool the lower atmosphere and increase snowfall in some areas.
  • Both major weather models now agree on a pronounced transition zone between rain and snow near Interstate 95 from about Washington to south of New York City. Along and east of I-95, more rain than snow is likely. Between 30 and 60 miles northwest, chances of significant snowfall increase.
  • Models are converging on the idea of ​​an initial period of snow when the storm begins Saturday in parts of the Mid-Atlantic, primarily west of I-95. It may only last a few hours, but the snow could fall enough to disrupt travel for a while. Thereafter, precipitation may turn to rain at lower elevations.

Schedule and possible totals

Friday night will see heavy rain and thunderstorms across parts of the Deep South and Southeast. As precipitation moves northeast into the Carolinas and southwest Virginia, freezing rain is possible over higher terrain. Moisture will slide over a shallow lip of frigid air moving down the mountains.

By dawn Saturday, snow will fall across eastern West Virginia and much of central and western Virginia. Washington, Baltimore and Philadelphia may see a few hours of snow, perhaps briefly heavy, before it turns to sleet and rain during the afternoon. However, that is not set in stone.

Snow will then reach the Northeast Saturday night and southern New England overnight. New York City could see several inches of snow, but a possible shift to sleet and rain may limit amounts there as the rain-snow line flirts with the city. Further inland, more snow is expected. The National Weather Service office serving New York City writes that confidence in snow accumulation is highest in the lower Hudson Valley and southern Connecticut.

There will be a sharp western cut of snowfall across central and western Pennsylvania and the southern Hudson Valley. In southern New England, rain and sleet may mix with snow within Interstate 495, but snow is likely, especially northwest of the Mass Pike and Interstate 84.

Boston and Providence could see several inches of snow before precipitation clears Sunday afternoon or evening, although the Weather Service office serving the region writes that “specific details are still unclear.” Providence may see less snow than Boston, especially if the European model projecting a stronger low is correct and more moisture is drawn toward the coast.

The center of the storm may remain too far east for significant snow across most of New Hampshire, Vermont, and inland Maine; Coastal Maine has a high chance of snow on Sunday.

The “sweet spot” of humidity that overlaps with cold air may not be very wide (only 50 miles or so), but it is more likely along the eastern slopes of the Appalachians, where there is a chance of falling between 6 and 10 inches of snow and the possibility of locally higher amounts.

Since the system will be moving quickly, the precipitation amounts will not be huge compared to other systems.

Washington may end up on the wet side of the rain-snow line

Everything indicates that Washington will be affected by the winter phase of the system. While plenty of precipitation will fall (the equivalent of about 0.75 inches of rain), temperatures in the mid-levels will warm as the storm passes. So after a brief period of wet snow from Saturday morning into the afternoon, sleet and then rain will begin to fall.

“The forecast for I-95 and points east is pretty clear as a mostly rainy event that could start out as a little snow with little to no accumulation,” said Wes Junker, winter weather expert with Capital Weather Gang. “Accumulations west of the city will depend on how far the rain-snow line migrates westward and the intensity of precipitation. “The greatest chance of significant snow will occur near and in the mountains.”

It’s not out of the question that Washington’s western suburbs could see an inch or two of snow before the change to sleet and rain.

Instead of quickly turning to rain Saturday afternoon, snow could continue over the Potomac Highlands and areas northwest of Montgomery and Loudoun counties into Saturday night. This could be a storm where Leesburg and especially Winchester see substantially more snow than areas within a county radius of the District.

Precipitation should end in the Washington area well before dawn on Sunday. The timing of the storm has accelerated, meaning confidence has increased that Sunday will be dry, aside from the possibility of passing rain or snow showers.

Some uncertainties remain, namely the specific trajectory and resistance of the low-pressure system. However, it will probably be better to finalize it on Wednesday night or Thursday. The main upper-air disturbance is moving toward the coast in the Pacific Northwest, and that means forecasters can launch weather balloons toward it. This greater sampling of data will allow for more accurate forecasts and models.

It is also unclear how strong the “50-50 minimum” will be. This is a low pressure system that will be established near 50 degrees north latitude and 50 degrees west longitude, near the maritime areas of Canada. That will draw in cold air, but probably not enough to cause a major snowstorm along most of the I-95 corridor.

Jason Samenow contributed to this report.

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