Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Observers reported collapsing in the snowpack Saturday. This indicates that you can still trigger an avalanche on a buried weak layer 1-3 feet deep. Overnight warming may stiffen the surface snow and increase the likelihood of triggering a slide. Error on the side of caution by sticking to slopes less than 35 degrees that are not connected to steeper terrain. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    Several parties reported collapsing in the snowpack Saturday. These signs of instability confirm that the mid-November buried weak layers remain troublesome. The weight of a rider or their snowmachine could trigger a slide on a buried weak layer resulting in a large dangerous avalanche. Warming temperatures overnight may increase this likelihood. Give yourself a wide margin of safety by sticking to slopes less than about 35 degrees and free of overhead hazards.

    (12/8/2022)

    Large column test that failed on isolation. Clear evidence the snowpack structure is still capable of propagating failures.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Thin reactive wind slabs were reported as recently as Friday. These wind-formed features appear more widespread in southern Glacier Park and the Flathead Range than in other areas. Warming temperatures overnight may have stiffened existing slabs and increased their likelihood of triggering. A stiffer, denser snow surface indicates that you have found a slab. Bypass this poor-quality surface in favor of the soft surface snow on slopes sheltered from the wind.

    (12/9/2022)

    Southwest winds have left the snow surface scalloped. Wind direction is from left to right in this image.

    Photo: Mark Dundas

Avalanche Discussion

Saturday’s half-dozen observations were from mid-elevation ridgelines in the Apgars, the Flathead Range, and outside the WMR boundary. Several parties reported isolated or widespread collapsing of the weak layer of mid-November. The last reported avalanche involving a buried layer of facets was one week ago. Still, feedback in the form of whumpfing is a clear sign it remains possible to trigger an avalanche 1-3 feet below the surface.

One group reported a substantial collapse that shook trees up to 200 feet away. This whumpf proves that avalanches can be triggered remotely - from gentler terrain above, below, and to the sides of steep slopes.

Warming temperatures overnight may lead to stiffer surface snow Sunday. Temperatures are in the mid to upper 20s at mid-elevation stations this morning. This is a big change from the cold air which we have enjoyed lately. There is uncertainty about how these temperatures will affect the cold, loose dry surface snow. Denser feeling snow will be a clue that the likelihood of triggering a slide has increased from what we've experienced over the past few days.

FAC encourages utilizing the terrain to minimize risk while dealing with a Persistent Slab problem. Besides utilizing slope angles, we encourage avoiding convexities because the combination of tension and lack of compressive support increases the chance of an avalanche.

The terrain outside the WMR ski area is easily accessible and draws many folks with limited avalanche knowledge or backcountry experience. There are numerous convexities outside of WMR, but today we will focus on one glaring example. Hellroaring Peak is just west of the current ski area boundary. The sizeable southeast face, visible from chair one, often is covered with ski or snowboard tracks. Most of the face is safe from avalanches due to its moderate slope angle. However, there is a convexity looker right responsible for incidents over the years. The most dramatic was In 1986 when a low snowpack prevented the grooming of the snowmobile trail across the face until February. By then, the old snow on the ground turned to depth hoar or sugar snow. Sure enough, as the groomer started across the road, he collapsed the weak layer and remotely triggered a slide that failed at the convexity. The resulting debris pushed the cat off the road. Fortunately, the operator turned the machine downhill, used his blade to push over small trees, and surfed his way down. The operator was not injured, and after a few repairs, the cat climbed up the debris to the road a week later. Check out these photos for perspective. Included is a skier-triggered slide on a faceted crust from 2009. 

Education - Our next Avalanche Awareness presentations are Tuesday, December 13, at Whistling Andy Distillery, Bigfork, and on Wednesday, December 14, at Penco Power Products, Kalispell. You can get more details about these free events on our events calendar.

Observations - Thanks to everyone who's been utilizing our new observation submission page. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as specific or vague as you want. Our new Observation View page highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives

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