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At a Glance A snowstorm slammed the northern Rockies.

Some parts of Montana had blizzard conditions and well over a foot of snow.

Wet snow and high winds led to tree damage and power outages.

Some lower elevations also picked up a record September snowfall. A historic September snowstorm blasted parts of the northern Rockies with heavy, wet snow and high winds, leading to power outages and tree damage, and was accompanied by record-cold temperatures for the end of September and early October.

Over a dozen locations in northern Montana picked up over a foot of snow . The highest snowfall total was 48 inches (4 feet) in Browning, Montana, about 105 miles northwest of Great Falls. East Glacier Park had measured 24 inches of snow.

In Great Falls, Montana, this snowstorm not only shattered September records, but it was also one of their heaviest snowstorms of all time.

Sept. 28 (9.7 inches) and Sept. 29 (9.6 inches) were the two heaviest September snowfall days on record in the city. The two-day total of 19.3 inches was second only to April 27-28, 2009 (24.2 inches) for the city's all-time heaviest two-day snowfall, the National Weather Service in Great Falls tweeted.

In an average winter season, it takes until the week before Christmas for Great Falls to tally 19.3 inches of seasonal snowfall.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/0929-sep-snow-recap.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/0929-sep-snow-recap.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/0929-sep-snow-recap.jpg?v=ap&w=980&h=551 800w" > Estimated snowfall from the Sept. 27-29, 2019 northern Rockies and Northwest snowstorm. The heaviest snowfall, generally well over 1 foot, is shown by the pink contours in Montana.

Tree limbs were reported down on "most, if not all, side streets" due to the weight of 16 inches of wet snow and winds in Choteau, Montana, about 45 miles northwest of Great Falls along the Rocky Mountain Front Range, according to a report relayed to NWS-Great Falls. Up to four-foot drifts were reported near Fairfield, Montana.

Missoula, Montana, also shattered its snowiest September record, picking up 1.7 inches on Sept. 29, topping the previous September record of 1.5 inches from 1934 in this western Montana city.

High winds downed trees around northwestern Montana's Flathead Lake, prompting a closing of State Highway 35 on the east side of the lake. Wind gusts from 40 to 60 mph were measured in Montana.

Spokane, Washington, had only its second measurable September snowfall in records dating to the late 19th century.

The National Weather Service said 1.9 inches of snowfall was recorded Sept. 28, and another 1.4 inches of snowfall was measured the following day. This storm total more than doubled the previous record September snow event there – 1.4 inches – which occurred on a single day, Sept. 23, 1926.

Tree limbs weighed down by wet snow were pushed into power lines, triggering some power outages in the metro area Saturday night, according to the NWS.

Up to 19 inches of snowfall was reported near the northeastern Washington town of Boyds, damaging a "significant amount of the surrounding trees," according to a report received by the NWS. Parts of the chimney of Idaho had measured up to 9 inches of wet snow, and numerous power outages were reported in northern Idaho, according to Avista Utilities.

In western Wyoming, up to a foot of snow was reported around Jackson Hole.

Snow even reached the valley floors around Reno, Nevada, on Sept. 28.

Given the combination of heavy, wet snow and winds, the Flathead Avalanche Center posted an unusual September advisory warning of dangerous wind slabs along the Northern Montana Rocky Mountain Front that could lead to very early season avalanches.

(MORE: When the First Snow Arrives Where You Live)

Montana had another early-fall snowstorm in early October 2017, which dumped over a foot of snow, and lead to widespread power outages and downed trees in northern Montana, including the city of Havre .

Why This Happened

The jet stream took a sharp, southward plunge from western Canada into the Northwest. That sent temperatures crashing well below average for this time of year.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/0923-snow-cold-northwest.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/0923-snow-cold-northwest.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/0923-snow-cold-northwest.jpg?v=ap&w=980&h=551 800w" > A southward plunge of the jet stream will drop temperatures well below average in a large part of the Northwest. Snow is forecast in the northern Rockies.

An upper-level low moved very slowly across the Pacific Northwest, which wrung out Pacific moisture into the cold air.

This taste of wintry weather was in stark contrast to the summerlike heat ongoing at the same time in portions of the East .

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.