Winter storm watches and warnings blanket a 1,700-mile swath across the central and eastern United States, heralding the approach of a significant storm system that could plaster 70 million Americans with snow.

A messy transition to mixed precipitation and rain will bring an unwelcome slop to a number of major cities along the Interstate 95 corridor, impeding travel and causing major disruptions for Martin Luther King Jr. Day weekend.

The snow was already falling across the Upper Midwest and Corn Belt on Friday morning, with snowfall rates exceeding an inch per hour in some locales. Parts of the Mid-South and Tennessee Valley are next in line, with cities such as St. Louis and Nashville at risk of a plowable snow. Flakes could even fly as far south as Tupelo, Miss., Huntsville, Ala., and Atlanta.

Then the storm shifts to the Eastern Seaboard on Sunday, delivering a mixed bag of precipitation to the coast and a dumping of heavy, wet snow inland. Ice could be a concern for a narrow strip of the Carolinas, including Charlotte.

After the storm departs late Monday, much colder air will build into the Mid-Atlantic and Northeast. Some areas may see rain or mixed precipitation flip back to snow. A flash freeze is possible on any untreated roadways that climbed above freezing.

Mid-South and Tennessee Valley

— Kansas City, Mo.: Winter weather advisory. Rain arrives around suppertime Friday, becoming snow as temperature fields collapse south around 10 or 11 p.m. Snow lasts until 4 or 5 a.m. before tapering off and exiting south and east. A general 0 to 2 inches west of town, 1 to 3 in the city and 2 to 4 in the eastern suburbs.

— Jonesboro, Ark: Winter storm watch. Rain begins by daybreak Saturday, with intermittent showers and downpours before a changeover to heavy, wet snow and isolated thunder during the evening. Cold air takes charge of the region and helps put down 1 to 3 inches before snow exits around 4 or 5 a.m. Sunday.

— Memphis: Winter storm watch. Rain arrives shortly before lunchtime Saturday, flipping to snow Saturday night and lasting a few hours as the storm’s chilly wraparound pivots north and east. Accumulations of 2 to 4 inches with locally higher amounts.

— Nashville: Winter storm watch. Rain begins Saturday evening and becomes snow as cold air pours into the region overnight. Highly uncertain forecast; the best moisture axis may reside south of Music City, delivering more snow to southern Tennessee and northern parts of Mississippi and Alabama. For now, Nashville should plan for 3 to 5 inches, with an outside shot of 7 inches.

— Tupelo, Miss.: Rain Saturday afternoon with a dose of snow early Sunday. Little to no accumulation expected, but an outside chance of up to 2 inches if the storm trends farther south.

— Huntsville, Ala.: Rain in the storm’s “warm sector” between midday Saturday and early Sunday. Then a transition to snow is possible. Accumulations uncertain, but an inch or more possible.

— Atlanta: Primarily a cold rain late Saturday night into Sunday, with a few flakes possible, especially north of town and outside the perimeter, on Sunday afternoon as the storm departs.

Appalachians and East Coast

— Asheville, N.C.: Winter storm watch. Snow arrives Saturday night and lasts most of Sunday. Accumulations of 6 to 10 inches in town, with up to 18 inches in the mountains above 4,000 feet elevation.

— Charlotte, N.C.: Winter storm watch. Showers of rain and/or snow becoming snow, sleet and freezing rain Saturday night. A slushy, messy half-inch or inch of snow and/or sleet with perhaps a quarter-inch of glaze. Dangerous driving conditions. Even more icing possible to the east of the Queen City near Monroe, Rock Hill and Albemarle.

— Roanoke, Va.: Winter storm watch. Snow begins Saturday night and lasts much of Sunday until the dry slot swings through. Accumulations of 5 to 9 inches with localized 11-inch amounts; a light glaze of ice possible.

— Pittsburgh: Winter storm watch. Snow showers Sunday afternoon/evening becoming steady overnight into Monday with accumulations of 4 to 9 inches likely.

— Washington, D.C.: Snow on Sunday afternoon and evening becoming a messy wintry mix overnight and transitioning to all rain. A slushy 1 to 3 inches, with 2 to 5 inches west of town before the changeover. A light glaze of ice possible. Considerably higher amounts west of the nation’s capital, with double-digit totals not unlikely in the Panhandle of Maryland and along Interstate 81.

— New York City: Rain on Sunday night with a few snowflakes mixed in initially. No accumulation whatsoever. Rain continues through Monday with highs in the lower 40s and breezy conditions before winding down in the afternoon.

— Boston: An inch or two of snow Sunday night before becoming all rain quickly and eroding any snow that fell. Highs rising into the mid 40s Monday with rain.

— Portland, Maine: Light snow Sunday night becoming rain on Monday and ending as a dose of snow Monday night. Accumulations of a couple inches, though most will be washed away.

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Snow began falling across North Dakota on Thursday night. By 6 a.m. Friday, half a foot was stacked in the town of Harvey, about 100 miles northeast of Bismarck. Fargo, along the intersection of Interstates 29 and 94, reported 2.5 inches. Sisseton, in northeastern South Dakota, had 3.5 inches on the ground.

The North Dakota Department of Transportation briefly implemented a “no travel advisory” for Minot and surrounding areas “due to near zero visibility and snow-covered roadways.” That has since been lifted.

The snow will wind down across the Dakotas and southwestern Minnesota between lunchtime in northern areas and Friday evening to the south. The storm will begin to intensify as it stomps through Iowa, dropping a broad 5 to 8 inches, with localized double-digit totals. Cities such as Des Moines may see jackpot totals there.

The storm continues to dip southeast over Missouri and Arkansas into the overnight hours and early Saturday. Rain will flip to heavy, wet snow in places such as St. Louis near daybreak Saturday and Jonesboro and Memphis by Saturday evening. It will last for only a few hours, but snowfall rates near an inch per hour could deliver an inch or two in short order. Above-freezing ground temperatures will make it tough to foster any accumulation other than on grassy surfaces, although the Ozarks could see up to 3 or 4 inches.

From there, the system angles east on Saturday night. A slug of moisture will arc counterclockwise around the low pressure center, spiraling into colder air entrenched over Tennessee and Kentucky. Most of Tennessee will see half a day’s worth of snow on Sunday, as will eastern Kentucky.

To the south and east, the Deep South will see mostly rain as the “warm nose” and conveyor belt of moisture streams in from the south, but falling temperatures in the storm’s comma-head “wraparound” may deliver some snow to northern Mississippi, Alabama and Georgia as the storm departs west to east Sunday.

Then the storm moves up the Interstate 95 stretch. To the east, the swirling low will drag north a slug of warm, moist air that will result in predominantly rain. West of the low’s track, heavy, wet snow will fall. Areas beneath the low will experience a front-end thump of snow that could entail snowfall rates in the 1 to 2 inch per hour range Sunday afternoon and evening; the warm nose, or a layer of mildness drawn in from the ocean around 5,000 feet above the ground, will cause a switch-over to rain.

Totals of 6 to 10 inches, with a few 10-to-14-inch amounts, are possible along the Interstate 81 corridor in Virginia, the Panhandle of Maryland and south-central Pennsylvania. There may be a sharp cutoff to the west due to an intrusion of dry air punching into the storm. Most of West Virginia, western Pennsylvania and New York State will see a plowable snowfall exceeding half a foot. Some lake-effect enhancement is possible east of Lakes Erie and Ontario.

In southern New England, most of the snow will be confined to inland areas and maximized in the higher elevations of the Worcester Hills and Berkshires. New Hampshire and Maine will see a good helping of snow into Monday, save for the immediate coastline. Vermont can expect a plowable snow, but the impeding dry slot may cut down on snow totals just a bit.

Even though the storm is already underway, downwind steering currents, which will ultimately determine the storm’s track, are still uncertain. Some of the computer models that meteorologists work with have exhibited a slight southwestward shift in their simulations of the storm. That could mean less snow for places such as Nashville and significantly less in Kentucky, and more for Kansas City, northern Mississippi and northern Alabama.

There is also a growing concern for some icing in western Virginia as the warm nose moves overhead Sunday night. Parts of the Carolinas will see significant icing as cold air drains down from the Appalachians and as milder, moisture-laden air rides up and over it, causing liquid rain that will freeze on the surface. It’s unclear to what extent Virginia experiences the same.