WEATHER NEWS: An early-season snowstorm is blanketing the Midwest to Northeast

The snow is coming in a three-part act, the prologue of which the atmosphere performed on Monday across the south-central United States. A narrow swath of heavy snow plastered Oklahoma with up to 7.3 inches in the town of Elk City, about 100 miles west of Oklahoma City. Now that same system is heading northeast.

Blast of cold swallowing Lower 48, with early-season snow for some

The wintry blitz is wrapped up within a blast of frigid air spilling south and east out of Canada, with quickly plummeting temperatures bringing a sudden seasonal reversal. Chicago hit 76 degrees on Thursday, only to peak at 36 on Saturday afternoon. Now, it’s under a winter-weather advisory.

Temperatures in Boston fell more than 30 degrees, from 76 on Friday to 44 on Sunday, and even Washington — where 10 of the first 12 days of the month climbed into the 70s — will struggle to escape the 40s. Snow is set to fall in the mountains west of these East Coast hubs.

Meanwhile, the National Weather Service in Buffalo is warning of the possibility of a “crippling” snowstorm for areas downwind of Lake Erie and Lake Ontario, from Thursday into the weekend.

On Monday morning, a storm system formed along a cold front in Oklahoma and Kansas. The system, energized by a high-altitude disturbance kicking east out of the Texas Panhandle, swirled chilly air into the Sooner State. That stacked the deck in favor of snow as moisture rode north along the front, resulting in a narrow, albeit intense, band of heavy snow.

That same system headed east, with snow on Tuesday from southern Illinois all the way through Wisconsin and into southern Manitoba and Ontario.

Meanwhile, moisture collecting on the front along the Gulf of Mexico coastline in Louisiana will blossom into its own new storm system, which will ride up the East Coast. The East Coast system will deliver “wraparound” snows on its cool air backside come Wednesday and Thursday. Then frosty westerly winds in its wake will blow lengthwise along Lakes Erie and Ontario, causing very heavy snows to their east.

Act I: Oklahoma snowstorm

Leading up to Monday’s snow in Oklahoma, forecasters at the National Weather Service in Norman had warned of a “high risk of disappointment.” There were a number of off-ramps that could have led to a “busted” forecast — and the razor-thin edge of the heaviest snow made communicating impacts even more difficult.

Despite the hurdles, a localized corridor of half a foot or more of snow materialized, impacting areas west of the Oklahoma City metro area. The jackpot was in Elk City, but Cheyenne in western Oklahoma saw 5.3 inches, and Sayre, Hinton, Geary and Clinton got four.

That proved Clinton’s earliest 4-inch snow on record, eclipsing the 4 inches that came down on Nov. 20, 1988.

Act II: Snow in the Midwest, Appalachians and Northeast

The snow has wound down in Oklahoma and on the Plains, but flakes are falling steadily in the Midwest. A broad 1 to 3 inches was expected in an area — the eastern two-thirds of Iowa, parts of Missouri and northern Illinois — blanketed by winter weather advisories through midday Tuesday. Downtown Chicago was encompassed in the current advisory, but the Windy City will see the bulk of its inch or two come down on Tuesday night on the storm’s backside.

Through Tuesday morning, about an inch had fallen just west of Chicago and around St. Louis, about 2 inches in Des Moines and 2 to 3 inches around Minneapolis.

As Tuesday wears on, wintry precipitation is forecast to spread over the Appalachians and interior northeast as the storm — currently headed toward the Ohio Valley — shifts its energy toward a new storm system forming along the East Coast.

Cold air is banking up in the mountains and will allow freezing rain to fall even in the mountains of western South Carolina on Tuesday, with the main hazard becoming snow in the high terrain of West Virginia and Virginia. Cumberland, Md., on Interstate 68, a key passage through the Appalachians, could be looking at 1 to 3 inches through Tuesday night; the bulk of any accumulation in the interior Mid-Atlantic will be relegated to locations above 1,000 feet and especially above 2,500 feet.

The snows will become more widespread north of the Mason-Dixon line, with a general 1 to 4 inches in northern Pennsylvania, most of New York state, the Berkshires in western Massachusetts and parts of Vermont and New Hampshire through Wednesday night. Lesser totals are expected in the hills northwest of Hartford, Conn. Three to five inches may fall Wednesday and Wednesday night in western Maine, with a half foot or more possible in Aroostook, Penobscot, Piscataquis and Somerset counties. That’s where a winter storm watch is in effect.

Act III: A major lake-effect snow dump

By Thursday, the low pressure system bringing snow to the interior Northeast will truck into the Canadian Maritimes, swinging its trailing cold front east and allowing cold air to spread toward the coast. At the same time, a dip in the jet stream, within which will be nestled a bone-chilling Canadian air mass at high altitudes, will become stuck over the Great Lakes.

That means cold, westerly to west-southwesterly flow a mile or two above the ground. That should entail cold wind blowing lengthwise down Lakes Erie and Ontario, which have water temperatures still in the 50s. The stark contrast should allow for robust lake-effect snow plumes to become established, with totals of several feet possible downwind. Snowfall rates of 1 to 3 inches per hour, whiteout conditions, thundersnow and blizzard conditions will be possible within the heaviest bands, which may only be a few miles wide. Unsurprisingly, if a given locations remains stuck in one of said bands for long enough, the totals could become extreme in short order.

The key time frame to watch would be Thursday through early Sunday.

“Total snow accumulations in this long duration event of MULTIPLE feet will be possible in the most persistent lake snows,” wrote the National Weather Service in Buffalo.