The German ICON model's depiction of how much snow may fall. (WeatherBell)

Four days into spring, a winter storm is quickly organizing across the interior Northeast. It’s set to drop more than half a foot of heavy, wet snow on inland areas, spelling treacherous travel and isolated power outages. Cities such as Boston, Philadelphia, Washington and New York will see all rain — but Hartford, Conn.; Concord, N.H.; Rutland, Vt., and Portland, Maine, will pick up a bit of snow. It’s a sneaky late-season snowmaker — and another coastal storm could be brewing later this week.

Light to moderate rain was sauntering up the coast from Virginia to New York City late Monday morning, another swath of precipitation stretched from the Alleghenies of Pennsylvania down through the Appalachians as far south as eastern Tennessee and the Carolinas. Each area of rain represents an impulse of energy and moisture, the two combining south and southeast of Southern New England and organizing into a storm.

It’s been an unusual winter for many in the Northeast, where unseasonable warmth and a largely snow-free pattern made it look as though Old Man Winter had thrown in the towel months ago. According to NewsCenter Maine meteorologist Ryan Breton, Portland, Maine, hasn’t seen a 6-inch snowstorm since Jan. 16 — more than two months ago! That may very well change Monday night as moderate to heavy snow overspreads the region.

Timing


A model simulation of rain and snow moving into the Northeast. (Pivotal Weather)

Rainfall already was entering the New York tri-state area Monday morning. Where only rain falls, some appreciable totals can be expected — an inch and a half on Long Island, with closer to an inch likely in the Big Apple.

In the higher elevations west of the Hudson Valley to the north in New York State, precipitation may mix with sleet and snow. Elevations above 1,500 feet should remain mostly snow, with all snow above 2,000 feet.

Southern New England

By early afternoon, moisture will be working into southern New England and probably will fall initially as snow along pockets of the Interstate 84 corridor in Connecticut and Massachusetts away from the immediate coastline. The flakes could fly in Hartford at first, as well as Springfield and Worcester, Mass.

There’s an outside chance even northern Rhode Island, including Providence, could break into some snow briefly if precipitation rates are heavy enough. Boston most likely will be snowing during the evening.

However, warm air aloft will work northward after sunset, abruptly switching everyone south of Interstate 90 to rain by 10 or 11 p.m.

Northern New England/New York State

Snow will be ongoing across most of Upstate New York, Vermont and New Hampshire away from the immediate Canadian border from late Monday afternoon through the evening.

Farther north, the heaviest bands look to target the New Hampshire Seacoast and coastal Maine, including Portland, between 9 p.m. and 1 a.m. There may be a “sweet spot” about 10 or 15 miles inland that winds up with a touch of thundersnow and/or 2-inch-per-hour snowfall rates. That would be along the “coastal front,” which divides cooler continental air from slightly milder air off the water. It’s in that zone that a localized 10-inch amount can’t be ruled out.

Thereafter, precipitation will continue to draw east-northeast, and while light to perhaps moderate waves of snow are likely along the Interstate 95 corridor in Maine through the wee hours of the morning — and possibly sunrise in Downeast Maine — it should be drawing to a close before the daylight hours Tuesday.

Amounts


The National Weather Service in Boston's prediction as to how much snow is likely to fall. (NWS)

If you’re looking for accumulating snow, drive about an hour north of New York City. That will probably be the dividing line between all rain and snow. In the Hudson Valley far enough inland, about 1 to 3 inches can be expected, with some 3- to 6-inch amounts above 1,500 feet.

In northern and central New York State, a widespread 2 to 4 inches looks likely, including between the Tug Hill Plateau, Capital District and the north country.

To the east, southern Connecticut, Rhode Island and Massachusetts will remain all rain. The Boston to Providence to Hartford corridor could see an inch before transitioning to rain. Northwestern Connecticut and the Berkshires could squeeze out some 1- to 4-inch amounts, as could the Worcester Hills. North of Route 2, a widespread 4 to 6 inches is likely.

Those amounts will taper quickly downward in central and northern Vermont and New Hampshire, which will sit on the northern fringe of the system’s moisture shield.

In southeast New Hampshire and adjacent southern Maine, 4 to 8 inches are expected, with a few 10-inch amounts possible if heavy snowfall rates materialize.

Elsewhere along coastal Maine, a general 3 to 5 inches are likely.

Limiting factors for snow

It will be hard for this system to overachieve or produce more snow than forecast, given the number of limiting factors in place. It is March, after all, which means the high sun angle and warm ground temperatures will conspire to melt snow before it can pile up too much. Moreover, an onshore breeze during most of the event will pump in milder marine air, cutting back on accumulations.

It’s tricky to pinpoint just how far inland this warmer air mass will penetrate, making determining how quickly snowfall totals ramp up in the interior challenging.

Moreover, air near the surface is extremely dry. That will make it tough for precipitation to fall — at least to start. It may take a couple hours for falling rain and snow to saturate the atmosphere enough that it’s able to make it to the ground. That could delay precipitation onset a couple of hours.

Another coastal storm?

Another system could pass near or southeast of New England late Wednesday into Thursday. Cold air will be in place inland, but right now the bulk of the moisture looks to pass a bit too far to the south for any snow. That could change — so check back for frequent updates as the event nears.