For the second time in two weeks, a powerful early-season winter storm is set to unleash double-digit snowfall totals across a wide swath of the northern Plains and Rockies through Friday. Along with heavy snow comes strong winds and near-blizzard conditions.
Winter storm warnings stretch from Wyoming and Montana through western Nebraska, then eastward into the Dakotas to the Canadian border. This is ahead of the sprawling storm system, an atmospheric mixer combining a shot of wintry air with a tongue of tropical moisture.
The National Weather Service in Bismarck, North Dakota, is referring to the system as a "potentially historic October winter storm."
So, what makes this storm so notable?
"I think, obviously, the magnitude of it, and it being the first storm of the season," said Patrick Ayd, a meteorologist at the Bismarck NWS office. "It's so early in the season. Normally we get to ease into things."
Despite this, Ayd noted that the past five to 10 years have featured several bouts of higher-end, early-season snow for the northern Plains, calling this event "not terribly unusual" in that sense.
The surface low that will bloom into the powerful winter storm is taking shape over Colorado, set to shunt northeastward as it develops beneath an invigorating disturbance approaching from the west. At the same time, a tongue of Gulf of Mexico moisture will be sucked into the developing low, providing the juice needed to produce huge snow totals.
The jet-stream pattern fueling this potential blizzard is so powerful that, by the weekend, the atmosphere could be more humid in Canada's Hudson Bay than in parts of the Southeastern United States.
Light to moderate snow was already falling across the hills and valleys of central and eastern Montana on Wednesday afternoon.
A developing area of snow is forecast to cover much of Wyoming and northern Colorado Wednesday evening before entering western Nebraska and parts of the Dakotas by predawn Thursday.
Things really ramp up after sunrise Thursday morning, when the stream of moisture-laden air from the south starts to kick in, acting as a conveyor belt to aid in snow production. As the storm system intensifies, and its trailing cold front crashes east, any ongoing rain in eastern North Dakota will flip to heavy, wet snow.
Snowfall rates of an inch or more per hour are a good bet at the height of the storm.
Meanwhile, winds near the low's "comma head" - the wraparound precipitation in the cold sector of a sprawling storm system, often shaped like a comma - could top 40 mph. Combine that with the moderate to locally heavy snow and it's likely to produce whiteouts in spots.
The National Weather Service noted that the storm "may create blizzard conditions."
All told, six- to eight-inch amounts, with localized snowfalls of a foot or more, are likely in eastern Colorado, Wyoming and central/eastern Montana - greatest on the east slopes leading up to the higher elevations. The same is true in extreme-northwestern Nebraska.
In western and central South Dakota, and central and eastern North Dakota, a widespread 10 to 14 inches is expected, with sporadic amounts topping 18 inches possible.
As the storm system pushes north into Canada over the weekend, a pinwheel of rain and snow showers is set to linger over the eastern Dakotas, Minnesota, Wisconsin and the Upper Peninsula of Michigan.
Although it may seem like an early onset, this part of the country is no stranger to prolific October snow.
A few years ago, Rapid City, South Dakota, picked up 19 inches on Oct. 4-5, 2013. Bismarck saw 15.9 inches in late October 1991, while Fargo, North Dakota, got nearly eight inches to usher in Halloween in 1951.
Even in places that don't see snow, a shot of cold air behind the storm will spill southward. The sharp cold front trailing the storm will bring an abrupt switch to fall for much of the country, including low temperatures in parts of the Deep South dipping into the 40s to start next week.
This article was written by Matthew Cappucci, a reporter for The Washington Post.