The early week storm system and cold front packed quite a punch for the Northern Rockies with most mountain ranges experiencing either heavy snow or damaging winds, and in some cases both!
The pattern has quieted down significantly since that time and a trend toward warmer temperatures will continue through the weekend and into early next week.
Warm and Dry this Weekend but Smoke arrives from Oregon and Washington
High pressure building in from the west will lead to a shift to above-average warmth from west to east across the mountains of Idaho-Montana-Wyoming. Mornings will continue to be chilly in mountain valleys as overnight inversions develop, but overall daytime temperatures will be quite nice.
Take a look at the projected temperature anomalies for Sunday afternoon, where many areas will be upwards of 10 degrees above average.
The downside to what would otherwise be a nice weekend is that a wind shift to west/northwest will lead to smoke arriving from wildfires in Oregon and Washington.
The smoke will initially move into Idaho on Saturday, before spreading into Montana and Western Wyoming on Saturday night and Sunday.
Here is the model projected smoke for early Saturday afternoon.
On Monday and Tuesday, winds aloft will shift to southwesterly, which will lift the heaviest smoke north into Montana and northern/western Idaho, while mountain ranges such as the Tetons and some of the east/central Idaho ranges should see some improvement.
Meanwhile, a slow-moving low pressure system will approach the Pacific Northwest early next week, and by Tuesday areas along and west of the Cascades will start to see some rain showers — and possibly a few days of rain showers — which will hopefully help out with the fire situation there.
Across the Northern Rockies, the above-average warmth will continue through at least Tuesday.
Cold Front Possible Along and East of the Divide Next Wednesday/Thursday
The latest medium range models are hinting that a cold front from the north could extend to the Continental Divide, bringing 1-2 days of cooler temperatures along with a chance of showers for eastern mountain ranges.
Glacier National Park will be in the best position to see moderate precipitation on Wednesday and Thursday, with lighter amounts south toward the Bitterroots, Bridgers, Madisons, Beartooths, and Bighorns.
Snow would be most likely across the higher elevations (and mid elevation east slopes) of Glacier as well, with a chance of lighter snow extending to the southern ranges along and east of the Divide as well.
There is still quite a bit of uncertainty regarding this cold front as it was not showing up even a day ago.
However, models are now trending farther west toward the Continental Divide, and that has been similar to the model trends with recent cold fronts, so I’m inclined to believe we could be in a similar situation here — but of course, with a much less intense shot of cold air compared to earlier this week.
Showers Possible across Most Mountain Ranges by the Weekend of the 19th-20th
A slow-moving trough of low pressure will be hung up near the Pacific Northwest for a good portion of next week, before finally progressing inland by the end of the week and weakening as it does so.
The result will be increasing showers chances from September 18th-22nd (roughly Friday-Monday) across the Northern Rockies. The weakening nature of the trough would point to a lighter precipitation event.
At this early stage, the mountains of northern/central Idaho and western Montana north of the Wyoming border look to have better precipitation chances, but that could always change.
Also, I wouldn’t rule out some lightning across the mountains either, especially on the warmer leading edge of the system.
A shot of colder air from the north may arrive on the back-edge of this system, which would increase the probability of high elevation snow showers by the 21st-22nd.
Long Range Looking Warmer and Drier for Late September
Beyond roughly September 23rd, high pressure is projected to strengthen again over the Western U.S., which would favor another stretch of warmer and drier weather across the Northern Rockies — a nice period of “Indian summer” conditions.
Meanwhile, an area of low pressure will be strengthening in the Gulf of Alaska around this time.
It may take some time for the high pressure to break down over the Western U.S., but I’m roughly eye-balling around the start of October that would could potentially see some more active weather reach the Northern Rockies if and when the high pressure manages to break down.