Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The weight of a rider or snowmachine may tip the balance and result in an avalanche failing on a weak layer buried 1-3 feet below the surface. Ride responsibly by choosing slopes 35 degrees or less in steepness and free of convexities. Fresh slabs of wind-drifted snow continue forming in favored locations. Default to sheltered slopes for a safer and higher quality experience.

Avalanche problems

  • Persistent Slabs

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

    Reports of collapsing and poor snow structures continue streaming in. It remains possible to trigger an avalanche on a buried weak layer 1-3’ below the surface. The most reliable way to manage this problem is with terrain selection. Choose slopes 35 degrees or less in steepness. Choose planar or concave slopes over those with a convexity. Steer around rocky areas where the snowpack is thin and more susceptible to triggering. Terrain with clean runouts free of trees and rocks may limit trauma if you trigger a slide.

    (12/9/2022)

    The notorious weak faceted crust is obvious in this image and identified by the blue arrow. This pit is at 5800' with the crust down 20 inches from the surface.

    Photo: Mark Dundas

  • Wind Slabs

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

    Riders encountered thin reactive wind slabs in southern Glacier Park Friday. Southwest winds continue forming slabs in locations experiencing recent snowfall. These wind-formed features are more widespread in southern Glacier Park and the Flathead Range than in other areas. Look for blowing snow as you gain elevation. 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) 30cm fresh wind slab avalanche - intentionally skier triggered while ski cutting

Avalanche Discussion

The layer is still a player… The FAC observation page contains 50 submissions, with nearly all reporting weak-faceted snow from the November dry spell. The slab above the weak layer is thickening and strengthening in many locations. Rob was in Kimmerly Basin teaching a motorized Level 1 avalanche class, and his group found a meter of snow on top of the weak layer. A more substantial slab limits the impact on that layer from the weight of a rider or their snowmachine. This, in turn, results in fewer avalanches and collapses than observed a week ago. However, reports of collapsing continue to stream in, with most recent observations noting the poor snowpack structure. It is becoming more difficult to trigger an avalanche, but due to the consolidating slab, the resulting slides may be surprisingly large and destructive. Our friends at the Gallatin Avalanche Center (Bozeman) had a close call Friday with a buried Persistent Weak Layer. One forecaster remotely triggered a large, deep slab avalanche while riding across a lower-angle slope below. The avalanche broke 3-6+' deep and 300' wide. One rider was caught and carried, not buried; luckily, nobody was injured.

Observations from the past few days mention excellent riding conditions but continuing wariness with our snowpack. Wednesday, the BNSF avalanche safety team reported a poor snowpack structure that appears to be widespread. They found a consolidating slab 1-3+ feet thick resting on top of a sometimes-reactive faceted layer. A large column test failed in isolation in the southern WF Range Thursday. Friday, the USGS initiated 3 audible snowpack collapses in isolated rocky areas in Stevens Canyon. I visited a nearby location and experienced widespread cracking that extended down 16" to the weak layer in areas sheltered from the wind below 6000'. Groups at Marion Lake and in the Apgars report a poor snowpack structure and isolated collapsing.

Check out The layer is still a player video that Sarah made. You can find it in the media below.

Wind slab is the other avalanche problem that has been on the list since we started forecasts a week ago. We keep trying to remove this problem from our product, but dribs and drabs of snow and breezy conditions continue to form slabs. These slabs are generally thin but can step down to a weak layer resulting in a large dangerous avalanche. Expect slabs to be more widespread in the Flathead Range and southern Glacier Park and less in the Swan and the Whitefish Range.

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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