Chances of snow accumulation greater than or equal to 4 inches. The colors on the map being at a 10-20 percent chance and grow in increments on 10 from there. (NOAA Weather Prediction Center)

This week’s winter storm is shaping up to be a travel nightmare for Wednesday, the day before Thanksgiving and the busiest travel day of the year.

A coating to several inches of snow could accumulate along the I-95 corridor on Wednesday. While temperatures have been unseasonably warm early this week, snow is still likely to accumulate along coastal interstates, especially during periods of heavy snowfall.

A Nor'easter that is expected to dump several inches of snow from Washington, D.C., to Boston is dampening holiday travel plans for many travelers this Thanksgiving. (Reuters)

Visibility is expected to drop below half a mile beginning on Wednesday morning as the storm moves northeast from Northern Virginia to southern New England. At times, snowfall rates could reach two inches per hour, especially in the inland areas away from the warm coast, making travel challenging, even on the interstates.

Related: Tips for Thanksgiving fliers

Airport delays and possibly cancellations are likely up and down the East Coast due to Wednesday’s storm.

Boston


Snow accumulation forecast from the National Weather Service. There is a strong gradient between accumulations of just 1 to 2 inches, and high accumulations of 8 to 10 inches. Boston itself is forecast to receive around 3 to 6 inches of snow, starting in the late afternoon on Wednesday. (NWS Boston)

Precipitation will begin as rain in Massachusetts early Wednesday morning but won’t really get cranking until the early afternoon. Very soon after the storm begins, rain will turn over to snow in inland Massachusetts. Boston will see snow mix in through the afternoon hours, before finally turning to all snow as the temperature along the coast drops to around the freezing mark in the evening. The heaviest snow is expected Wednesday afternoon and early evening.

The storm will begin to wane on Wednesday night, and the worst will have cleared out of Massachusetts by Thursday morning, though light flurries could linger through Thanksgiving Day.

Potential accumulations vary across Massachusetts. As much as 16 inches of snow could end up falling inland, while toward the coast the accumulation will drop to 1 to 3 inches, where it likely won’t be below freezing early enough for larger snow totals. In Boston itself, expect accumulations around 3 to 6 inches. However, the National Weather Service in Boston is giving the city about a 50 percent chance of seeing snow accumulation greater than 6 inches.

Watches, warnings, and advisories from NWS Boston. (NWS)
Watches, warnings, and advisories from NWS Boston. (NWS)

Update at 3:05 p.m.: The winter storm warning has been extended east, and nearly includes Boston itself, though not quite. A winter weather advisory has been issued for far eastern Massachusetts and northern Rhode Island for as much as 3 to 6 inches.

In addition to the winter storm watches and warnings, a wind advisory has been issued for coastal Plymouth County, Cape Cod and the islands around Cape Cod for sustained winds of 25 to 35 mph, with gusts up to 50 mph on Wednesday.

Whom to follow: Eric Fisher covers Boston area weather for WBZ.

New York City area


Snow accumulation forecast from the National Weather Service. (NWS New York)

Update at 3:45 p.m.: The National Weather Service has decreased their “most likely” snowfall forecast (above) over the NYC area by about 1 to 2 inches.

The storm begins in the NYC area around daybreak on Wednesday. Precipitation will start as rain and quickly change over to snow away from the coast. It will take longer for this transition to happen near the water, an in particular in New York City itself. However, as the temperature drops in the city, snow will gradually mix in before changing to all snow in the evening. The storm will begin to decrease in intensity after 7 p.m. on Wednesday, and will have cleared out of the area by Thursday morning.

Accumulations forecasts climb rapidly as you move west, away from the coast. West of I-95 could see  6 to 8 inches of snow, while the boroughs could see anywhere from 2 to 6 inches. In general, the further south and east you are, the less snow you will accumulate (e.g. Brooklyn will probably see lower snow totals than the Bronx). Manhattan is probably looking at up to 4 inches.

However, as the Weather Service in New York has pointed out, this is “undoubtedly one of the more challenging forecasts.”

Watches, warnings, and advisories in effect for the NYC area. (NWS)

winter storm watch is in effect for much of the New York city area, though it does not extend onto Long Island beyond northern Nassau County. The watch is in effect from Wednesday morning through Thursday morning for snow accumulations of 4 to 8 inches. (Again, the farther east and south you are, the more likely it is you’ll see totals on the lower end of that range.)

West of I-95, a winter storm warning is in effect for portions of east central New York, extending east through inland portions of Connecticut and Rhode Island for accumulations of 6 to 16 inches of snow. The Weather Service also warns of snowfall rates up to two inches per hour, which will severely reduce visibility on the roads.

Whom to follow: Try @nymetrowx, or the meteorologists at ABC — @ginger_zee and @robmarciano. They are technically national meteorologists, but they are located in New York, so they will probably have some good info.

Philadelphia

Snow accumulation forecast for the Philadelphia area from the National Weather Service. (NWS) Snow accumulation forecast for the Philadelphia area from the National Weather Service. (NWS)

Update at 2:55 p.m.: The National Weather Service in Mount Holly has nudged up their forecast snow accumulations for southeast Pennsylvania and New Jersey, including the city of Philadelphia. They are now calling for as much as 10 to 14 inches in the southern Poconos and northwest New Jersey.

Precipitation will begin as rain in the Philadelphia area early on Wednesday morning and last through the midafternoon, at which point rain will turn into snow. Farther inland in Pennsylvania and inland New Jersey, the snow will mix in earlier in the day, possibly in the late morning.

The worst of the storm will occur in the early afternoon hours, but will begin to wane in intensity by the early evening, and move out of the area overnight.

Snow accumulation is expected to be slightly less in the Philadelphia area than the cities up north — around 2 to 4 inches is forecast to accumulate around the city.

Farther inland in southeastern Pennsylvania and northwestern New Jersey, the forecast grows to 10 to 14 inches.

On Tuesday, the National Weather Service in Mount Holly suggested that travelers consider altering their plans based on the storm timing. “Suggest travel into eastern Pennsylvania and northwest New Jersey be completed no later than 7 a.m. on Wednesday, or wait until after 7 p.m. Wednesday night,” they write (though I am paraphrasing). “It’s that 12-hour window that is going to become a significant travel problem, especially in the hilly areas.”

Watches, warnings, and advisories in effect for the Philadelphia and New Jersey area. (NWS)

A winter storm warning is in effect for much of eastern Pennsylvania, including Philadelphia, and northwestern New Jersey starting Wednesday morning and lasting through Wednesday night. Snow will be wet in the city and along I-95, though the snow could still be hazardous on the roadways and, at the very least, will cause travel delays. The Weather Service also warns of the possibility that wet, heavy snow could bring down some tree limbs, which could lead to a few power outages.

Whom to follow: Gary Szatkowski of the Mount Holly National Weather Service office.

Washington, D.C.-Baltimore


Second call for Wednesday snow amounts, issued 11:30 a.m. Wednesday (Capital Weather Gang)

D.C. Details: Everything you need to know about Wednesday’s winter storm

Rain begins in the D.C.-Baltimore region in the early morning hours, between 2 and 5 a.m. Temperatures are expected to remain above the freezing point for most of the day in the immediate metro areas and east of I-95, though rain will have changed over to snow by late morning or so.

In D.C. and Baltimore, accumulations are likely to reach a coating to 2 inches. Again, northwest will be higher, southeast will be lower.

Update at 11:00 a.m.: The winter storm watch has been upgraded to a warning for northern Virginia and western Maryland for accumulations of 3 to 6 inches below elevations of 1,500 feet, and 6 to 10 inches above 1,500 feet. A winter weather advisory has been issued for counties west of I-95.

A winter storm warning and a winter weather advisory is in effect west of I-95. (NWS modified by CWG)
A winter storm warning and a winter weather advisory is in effect west of I-95. (NWS modified by CWG)

The areas likely to see the most substantial snow and hazardous driving conditions are from northern Montgomery County through eastern Loudoun and northern Fauquier County and to the north and west. The worst traveling time will be from midmorning to midafternoon, when snowfall could reduce visibility on the roads. Roads will also become slippery as the snow begins to stick in the higher elevations. In particular, the Weather Service calls out interstates 81, 70, 83, 66 and 64 as roads on which to use extreme caution.

Power outages are possible in areas where heavy snow could bring down tree limbs.

The worst of the storm should be over by the evening hours.

You can follow all of our winter storm updates here on the blog, or on Twitter.

Jason Samenow contributed to this post.

A Nor'easter that is expected to dump several inches of snow from Washington, D.C., to Boston is dampening holiday travel plans for many travelers this Thanksgiving. (Reuters)