Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Warm temperatures and overcast skies will increase the likelihood of wet loose avalanches on all aspects today. North aspects may become wet for the first time leading to a round of wet loose avalanches, with some large enough to bury and injure a person. Warm temperatures may also increase the possibility of hard, persistent slab avalanches. Manage both of these problems by sticking to slopes less than 35 degrees if you do not feel a supportable crust, or if the snow surface feels wet.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Most remote weather stations last night did not go below freezing. Consistent warm temperatures may increase the likelihood of hard, persistent slab avalanches failing 3 to 6 feet deep. For this same reason, we also widened the distribution back to all aspects at middle and upper elevations. Stick to slopes less than 35 degrees if you do not feel a supportable crust under your feet. If you do feel a supportable crust, feel more confident stepping out into steeper terrain.

    (3/4/2021) A very large Persistent Slab avalanche on an SW aspect in southern Glacier Park. Warm temperatures and solar radiation triggered this slide.

  • Loose Wet

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

    Warm temperatures and overcast skies likely kept the snowpack from refreezing overnight. If this proves to be true, and this weather pattern continues, expect to see wet loose avalanches on all aspects. They will be larger and more hazardous on north aspects where the snow surface is becoming wet for the first time. If you feel a crust this morning, expect a window of stable avalanche conditions. If the crust is broken down and you feel wet snow or see rollerballs, plan to be off and out from underneath terrain steeper than 35 degrees.

    (3/7/2021) Natural wet loose running through not so obvious avalanche terrain.

  • Cornices

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

    Observers continue to report large cracks on ridge lines where cornices are beginning to un-root themselves. There is a growing concern for cornices to fail with warm temperatures. Cornice fall is an obvious and manageable hazard: plan your ascent and descent to avoid being underneath the overhanging school buses that can spontaneously fail and cause a significant amount of harm in of-themselves. Give ridgelines an extra-wide berth to avoid accidentally walking out onto them. The last known hard slab avalanche was triggered by a cornice fall. 

    (3/13/2021) Give the edge of ridgelines a wide berth.

Avalanche Discussion

Remote weather stations in all three ranges remained warm overnight. Low temperatures at Big Mountain was 32 degrees F, Tunnel Ridge in the Flathead Range was 36 degrees F, and Noisy Basin in the Swan Range was 35 degrees F. Looking at satellite imagery and sky conditions early this morning, I expect that cloud cover rolled in and most areas are overcast. This cloud cover will prevent the snowpack from being able to shed heat into the atmosphere, creating a greenhouse effect. If this is the case, then most areas did not have received a refreeze overnight, or if they did, then it would be superficial and will break down quickly.

The main difference between today and Sunday will be the likelihood of wet loose avalanches. If green housing does occur, I wouldn’t be surprised to see a round of natural avalanches on north aspects where dry snow is becoming wet for the first time. If you don’t feel a crust this morning, plan to dial back your terrain choices. Build-in options to your plan by adjusting to surface conditions. Is it refrozen and supportable? If yes, then feel confident stepping out into steeper terrain. Is the surface wet, and are you sinking in up to your knee? If yes to this question, then plan to stay out of avalanche terrain today.

On top of all this, don't forget about the possibility of glide avalanches. Warm temperatures and little refreeze the past two nights have increased our concern for a glide crack to fail as a full-depth avalanche. We received a report yesterday of the possibility of this happening in the southern Whitefish Range sometime this week. A glide avalanche would take out the entire season's snowpack and likely be unsurvivable. Manage this hazard by identifying where glide cracks exist and avoid the terrain below them. The vast majority of observed glide cracks are on southeast aspects.

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