Well we made it to September, and that means its time to start looking at the weather models on a daily basis. The northern Rockies are usually the first place to get any real snow, due to the jet stream starting to sag farther south during the fall, and this year will be no different. We had a few dustings in Colorado and Big Sky last week and now today, but it looks like the first good thump of snow will be in SW Montana tomorrow to Wednesday. The mountains of Western Alberta as well as high elevations in Northern Utah could see some flakes too.
Keys to the Chase
The snow will start falling tonight in Alberta and continue off and on through tomorrow. Interior BC should see some flakes as well. A few inches are possible in the higher elevations around Banff. Tomorrow afternoon through Thursday the focus shifts south with the jackpot zone in SW Montana, specifically the Beartooth and Absoroka range. Here, over a foot is possible above 12k feet. Beartooth Pass, near the summer ski resort Beartooth Basin, will likely see 4-8\" by Thursday. Amounts will decrease with elevation from there. The southern part of the Absarokas and the Wind River ranges in Wyoming should also see minor snow accumulations during this period, along with the Uintas in Northern Utah, where a few inches could pile up at the upper elevations of these ranges. So, if you're giddy like a kid on christmas about your first chance to see accumulating snow, you now know where to go. Here is a little snowmap to whet your appetite.
(image courtesy of Weatherbell)
Details for the Weathernerds
It's been generally very warm over the Western US for much of July and August, but we finally have, at least temporarily, a shift in the pattern. Below you can see a broad trough over the US, which is bringing a relief from the warm weather and chances for precipitation, including snow, as well. You can see the trough progressing eastward across the northwestern part of the country, with some solid lift, (needed for precipitation), associated with the upper level low moving across southern Montana, Utah, and Wyoming on Wednesday..
(image courtesy of Tropical Tidbits)
Around hour 54 you can see the low pressure close off over eastern Montana, and then slowly move east. At the same time, a surface low will form over eastern Montana as well, resulting in a vertically stacked system, which is indicative of weakening and oftentimes a cold pool aloft. Below is a gif of the ~10k foot temperatures, where you can see cold air associated with the vertically stacked low. Initially, there is some cooler air in the NW US, but, as the low closes off and becomes vertically stacked, you can see the colder air start to almost break off from the region where it started, and instead follow along the vertically stacked system. This will provide the cold temperatures responsible for snow at higher elevations, as the 10k temperatures are below freezing. The combination of lift from the upper level low and cold temperatures will create the environment where snow is possible over the next few days.
(image courtesy of Tropical Tidbits)
Towards the end of the first gif you can see another upper level trough moving over the region. Beyond that, although not pictured, the models are indicating that a third upper level low pressure could affect the western US. This would result in continued cooler temps and additional chances for high elevation snow. Stay tuned for updates.
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