In Minneapolis, a hefty 7.9 inches fell, becoming the heaviest snowstorm recorded in the city this early in the season. On Tuesday, Eau Claire, Wis., about 75 miles east, picked up 6.9 inches, becoming its snowiest October day on record.
That storm had dropped 13.3 inches on Great Falls, Mont., over the weekend, the heaviest calendar-day October total on record measured in the city. Its October monthly average is 1.9 inches.
The same impressive system even brought dangerous snow squalls to central Iowa, leading to accidents on Interstates 80 and 35 and dropping 2.2 inches of snow on Des Moines. Areas just north of the city toward Ankeny picked up six to eight inches in the narrow band.
Now, many of the same parts of the Upper Midwest, Northern Plains and Northern Tier are under winter weather advisories and winter storm watches. They’re expecting a second round of snow later this week, with a third potentially brewing as well.
It’s part of an active pattern tied to a developing La Niña, which increases the odds of a cold and snowy winter in parts of the northern United States.
More accumulating snow on the way in the north-central U.S.
A pocket of cold air at high altitudes was already gathering over the Northern Rockies and Pacific Northwest during the midweek, set to help develop a low pressure center east of the Palmer Divide toward the Sand Hills of western Nebraska on Thursday. The quick-hitting disturbance will scurry northeastward along a cold front, passing over the Great Lakes and into Ontario and Quebec on Friday.
That system will switch winds around from the northwest and provide a reinforcing cold shot in its wake. A stream of moisture from the south will “overrun” cold air to the north, falling as snow north of the low’s center.
Pockets of light to briefly moderate snow had already broken out across Montana and portions of South Dakota during the afternoon hours Wednesday. Snow in those areas will increase in area coverage and intensity Wednesday evening and night, becoming moderate near the South Dakota-North Dakota line. The snow should just be shifting east into the James Valley by dawn Thursday, lingering all day to the west.
A half-foot or more of snow is possible in northeast Montana north of Highway 2, with slightly lesser amounts between three and six inches farther south and east — such as on the Fort Peck Indian Reservation.
The Crow Reservation in southern Montana could get plastered, as will likely the Bighorn National Forest in the high terrain of northern Wyoming. A few one-foot totals are likely there.
A strip of heavy snow is also likely through the Dakotas and into Minnesota.
In Minnesota, the snow — which will fall Thursday afternoon into Friday — might largely miss Minneapolis to the north. Currently, the Twin Cities are not under a winter weather advisory, although areas in northern and central Minnesota are expecting five to 10 inches of snow.
Northern Wisconsin and the western Upper Peninsula of Michigan will be fringed by some snow, too, as the system departs into Canada.
Additional snow possible next week
A stronger cold front will sag southeast across the central United States late in the weekend, trailing a low pressure system sliding southeast from the Pacific Northwest and slinging east across the Plains and Great Lakes. That will bring another period of snow to the Northern Rockies late Friday and Saturday, and the Northern Plains and Upper Midwest, perhaps again including Minneapolis, on Sunday.
Greater uncertainty exists in Nebraska, northern/western Oklahoma, Kansas and especially Iowa, where it is still too soon to say with confidence whether snow will become an issue. The American GFS model is more aggressive in simulating a stronger cold front with better access to moisture, depicting accumulating snow in a more widespread area; the European model is a bit tepid.
An active wintry pattern
The ongoing spate of snowy systems is courtesy of an active pattern targeting the northern United States, with loose ties to a developing La Niña. El Niño and La Niña are both known to influence wintertime precipitation and snow totals by affecting the position of the jet stream.
La Niña is characterized by anomalous cooling of waters in the eastern tropical Pacific. Through a chain reaction effect, that helps establish high pressure off the West Coast, which sends the jet stream surging north over Alaska and the Aleutians.
When the jet dives southward again over the Canadian Rockies and northwestern/north central Lower 48, it tugs along with it outbreaks of cold air. La Niña years also typically feature more moisture being trucked in over the Northern Tier, making it easier to conjure up hefty doses of snow.
Temperatures early next week are forecast to plummet from the West Coast to the Upper Midwest as the jet stream takes an especially sharp plunge. The Rockies and the western Plains may be hit particularly hard, with temperatures up to 20 to 40 degrees colder than average.