In the Flathead Range and Glacier Park, the snowpack took a hard hit last weekend and still needs time to recover. Use caution: You can trigger an avalanche that breaks several feet thick and surprisingly wide on early-season weak layers. You are most likely to trigger a slide from a shallow, rocky area or a steep rollover. Default to planar, lower angle terrain if your snowpack assessments give you uncertainty.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
The higher you go in elevation to a snowpack that is more attractive for riding, the more likely you are to encounter a lingering persistent slab. Weak layers buried 2 to 4 feet deep are still adjusting from last weekend's dramatic load, which spurred several natural D3 avalanches. Steering away from shallow, rocky areas helps keep you away from areas where the snowpack might be thinner or weaker. We have also triggered a few collapses in the past month while digging down through the crusts - the same type of disturbance you put on the snowpack when your sled gets stuck and you dig it out. Watch your partners ride steep slopes or free their sleds up from a safe location away from the runout of a potentially large avalanche.
The threat of triggering a persistent slab is most pronounced the further north and east you go, geographically speaking, in our forecast area. This terrain held the coldest, weakest snowpack through November and was subsequently hit the hardest by last weekend's storm.
Glacier National Park and Flathead Range: Flattop Snotel, northeast of Lake McDonald, saw 4.6" of SWE through the weekend: more than 4 times the water weight that fell in the Whitefish Range and about 8 times the load on the Swan Range. Waterton Lakes National Park, just across the border from Glacier, reported a handful of natural D3's as recently as Sunday. Locally, Mt. Furlong in John F. Stevens Canyon and Mountain Nyack, in the Flathead Range, both produced a D3's during or shortly after the storm (See observation). With more alpine terrain which receives more dramatic wind loading, paired with more continuous weak layers from early season, the potential for widely propagating and more destructive slides is also larger in these areas.
Swan Range: Meanwhile, in the Swan Range, Noisy Basin only picked up 0.6" of SWE from last weekend's storm on a snowpack which has been showing us fewer signs of instability underfoot and in stability tests all season. Our last reported collapse was a week ago, and we have yet to note an avalanche failing on buried crusts or facets this winter. Persistent weak layers still exist in the snowpack, but the problem appears to be less reactive and more isolated. Isolated means there are only a few places you can get into trouble. It doesn't mean you have a hall pass to turn off your brain or stop practicing safe travel protocols.
Whitefish Range: And finally the Whitefish Range, we have some blend between the two. The weekend storm produced 0.8" SWE at Stahl and 1.3" SWE at Big Mountain. The snowpack has been talking to us more often than in the Swan Range with numerous collapses and shooting cracks. However, we haven't observed much for avalanche activity on buried crust layers - only one reported slide on early season weak layers this month. Ski patrol at WMR has been testing these layers with explosives without results.
In summary, persistent slab concerns and the avalanche danger are easing and will continue to trend down during the quiet weather in store over the next few days. Avalanches breaking several feet thick are more likely, and will be more destructive in Glacier Park.
Santa will be flying his sleigh through quiet weather this Christmas. The jet stream has sagged well south of us, leaving NW Montana in a weak low-pressure system. Winds and temperatures are thankfully trending down. Expect a few flurries on Christmas Eve giving way to drier conditions on Christmas Day.
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Mostly Cloudy | Mostly Cloudy | Mostly Cloudy |
| Temperatures: | 23 to 28 deg. F. | 13 to 18 deg. F. | 19 to 24 deg. F. |
| Wind Direction: | Southwest | Southwest | West |
| Wind Speed: | 5 to 15 | 5 to 15 | 0 to 10 |
| Snowfall: | 0" to 1" in. | 0" in. | 0" in. |
| Snow Line: | 2500' | 1500' | 500' |
This forecast applies only to backcountry areas outside established ski area boundaries. The forecast describes general avalanche conditions and local variations always occur. This forecast expires at midnight on the posted day unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.
