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Blizzard To Slam Northern Rockies This Weekend


The northern Rocky Mountains are about to get a harsh blow from Mother Nature. A potential blizzard-like storm could shut down roads and knock out power in many high-elevation areas. The National Weather Service (NWS) has already issued a Winter Storm Watch for parts of Montana, mostly along and north of I-90 and west of I-15, where the worst of the storm may hit. However, the Watch may be expanded to include other areas of Montana and/or neighboring states. Shipper may want to plan now in order to get ahead of the storm.

SONAR Critical Events: Wednesday, September 25, 11 a.m. EDT

The set-up

A strong Canadian cold front will likely move through north-central and central Montana on Friday, September 27, lingering over southwestern Montana the next day. During this time, a low pressure center will move southward into the Pacific Northwest, sending plenty of moisture into the northern Rockies. This will likely bring rain showers and mountain snow showers to the region Friday into Friday night, with a slight chance of afternoon thunderstorms.

Temperatures will gradually begin to cool with highs in the 40s and 50s across northwestern Montana by Friday, lows in the mid-20s to mid-30s. The cold air will continue to push south behind the front on Saturday, causing more widespread accumulating snow in the mountains of northwestern Montana, rain in the southwestern valleys, and a mix of rain and snow in the northern plains. The coldest air over the plains will initially be along the Rocky Mountain Front, making that area most likely to see accumulating wet snow on the plains.

Snowfall amounts

The Rocky Mountain Front and adjacent plains are areas of focus for the Winter Storm Watch, which for now is in place from Friday evening through Sunday afternoon, September 29. Total snow accumulations in these areas could reach one to three feet, with locally higher amounts on the tallest peaks. Wind gusts of 40 mph across the Rocky Mountain Front and west over the Continental Divide will create periods of blizzard/white-out conditions. Adding insult to injury – the storm may produce record or near-record cold temperatures in the teens and 20s, along with wind chills of zero to 15° above zero.

The nearby city of Great Falls isn't in the Winter Storm Watch at this time. However, Jason Anglin, a meteorologist with the NWS in Great Falls, told FreightWaves he expects that city to receive six to eight inches of snow. Anglin also noted that this outlook could change. The historical average three-day total for this time of year is less than half an inch.

Besides treacherous road conditions, this early season storm has the potential to cause other extreme impacts such as widespread loss of electricity due to downed power lines. In addition, widespread significant tree damage is possible with heavy, wet snow and strong winds weighing down trees that have a lot of foliage.

Weekend #WinterStorm UPDATE: it looks like valley #snow is becoming more likely. Accumulations will be minimal, but for so early in the season, it will be a major impact, along w/all the other impacts we'll see. Suffice to say: this will be a historic storm. #mtwx #idwx pic.twitter.com/yRN6niqeST

— NWS Missoula (@NWSMissoula) September 25, 2019

Making history?

According to the NWS, this early season winter-like storm has the potential to set a new benchmark for snow accumulations, cold temperatures, and resulting impacts for parts of the Northern Rockies and the Rocky Mountain Front. A similar storm in 1934 produced prolific amounts of snow in late September over north-central Montana.

Anglin said the 1934 storm dropped a three-day snowfall total of 13.2 inches in Great Falls (elevation 3,675 feet) and 28.0 inches in Conrad (elevation 3,517 feet), about 60 miles to the northwest. He also mentioned that the last significant September snowstorm to hit Great Falls was in 1988, when 8.4 inches came down over a three-day period. Anglin explained that if a storm of this magnitude were to pan out, it would likely happen early or late in the season because this is when the polar jet stream – the winds aloft that steer weather systems – is most active.

Other areas of Big Sky country – Bad Rock Canyon, Essex, Highway 83 from Bigfork to SwanLake, Marias Pass and Polebridge – may also see total mountain snow accumulations of one to three feet, with valley totals of three to nine inches. Places such as Butte, US-12 from Garrison to Elliston, Homestake Pass, MacDonald Pass and I-90 east from Missoula to Bearmouth could be hit with 16 to 25 inches. Winds in all of these spots could gust as high as 40 mph.

Precipitation should gradually decrease across the region next Monday, September 30 into Tuesday, October 1 as the low pressure center moves farther to the south away from the area.

NWS forecast confidence is high at this time regarding snowfall accumulations, wind strength and expected impacts. There is low to moderate confidence on the timing of the onset and end of this winter storm event. Look for updates on the FreightWaves social media accounts.

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