Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 2 years ago.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

Highlights

It is possible to trigger a slab avalanche where you find 8+ inches of new or drifted snow. Slopes downwind of ridges and saddles will be the most dangerous. You can reduce the chances of triggering a large slab avalanche by sticking to slopes sheltered from the wind or choosing slopes facing south. 

Avalanche problems

  • Wind Slabs

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

    Avoid getting caught in a stiff slab of wind-drifted snow by sticking to slopes sheltered from the wind. Slabs of drifted snow will be more common on the downwind side of ridges and gullies. You may also find sensitive slabs on cross-loaded terrain features further down the slope. Dune-shaped or pillowy-looking features are visual clues to steer around. Utilize small and inconsequential test slopes with a spotter to test the sensitivity of recently drifted snow.

    On shaded aspects, slabs rest on a layer of surface hoar and near surface facets. Slabs may be remotely triggered and can propagate wide distances. The sun destroyed this weak layer on solar aspects before it was buried, and field observations generally describe a more stable snowpack structure on those aspects.

    (12/2/2024)

    Here is an example of mid-slope crossloading. The wind features on this slope indicate that the wind was transporting snow from left to right. 

    Photo: Michael Reavis

Avalanche Discussion

Saturday’s storm buried a weak layer of surface hoar across the region. However, varying snow totals left different avalanche problems in different zones. Today in the Whitefish Range, we transitioned from Storm Slab to Persistent Slab. Elsewhere, Wind Slab remains the primary hazard. Here is the rationale:

Storm totals favored the northern part of the forecast area. The central and northern Whitefish Range received 1 to 1.5 feet of new snow. Field observations in this area confirmed a natural avalanche cycle. Blase was in the southern Whitefish Range yesterday (Monday) and found generally stable avalanche conditions at mid-elevations due to the lack of recent snowfall. 

Flattop weather station in central Glacier National Park picked up 1.7 inches of snow water equivalent (SWE) and a change in snowpack height of a foot. Although we haven’t received observations from the Lake McDonald zone, we expect similar conditions to those in the northern Whitefish Range. Tunnel Ridge in the Flathead Range picked up 5 inches of new snow. The storm mostly skunked the Swan Range, but we have yet to receive reports from the northern part of the range. Generally speaking, problematic areas are where 8+ inches of new or drifted snow fell. This will be more common the higher you climb and in wind-loaded terrain.  

Saturday’s storm buried a variety of surfaces. Clear skies and cold nights weakened the snow surface on shaded aspects, and the sun cooked solar aspects leaving behind a sun crust. We are most concerned about shaded aspects where a well-documented layer of surface hoar exists. Shaded aspects appear to be the hotspot for natural avalanche activity, and a crown profile confirmed surface hoar as the weak layer. 

Did you hear about the app? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can win debates about the avalanche problems right in the backcountry or submit an obs while driving home. 

Registration is open for this season's avalanche courses. Get some learning done!  There's an Avalanche Awareness class on Wednesday, December 11th, at 6:00 pm at the Stonefly Lounge in Coram.

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