Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

An Avalanche Warning is in effect. Deadly natural and human triggered avalanches are very likely. These can break widely on buried weak layers or within the storm snow. Avalanches will be larger and more destructive at higher elevations. Expect them to entrain lots of debris and run far and fast. These are very dangerous conditions. Avoid traveling on, or under, slopes steeper than about 30 degrees.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    Over the past week, riders have reported triggering avalanches on upper elevation slopes and on shaded, mid-elevation slopes.  As new and drifted snow have thickened slabs, the reported slides have grown wider, deeper, and more dangerous. The situation is even more serious now that new snow and wind have stiffened slabs and loaded layers of buried surface hoar and facets to their tipping points. Avalanches that fail in the storm snow are likely to step down and trigger these deeper layers.  Avalanches that start up high have a lot of snow they can entrain as they run down the slope.  The results can be deadly.

    (2/3/2021) Slide remotely triggered by skier at tree. 6600 feet, north-facing slope. The slide propagated around the corner and wider on the slope below.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    New snow has accumulated rapidly. On Thursday, soft slabs and sluffs were triggered by riders and natural cornice fall. Conditions have deteriorated and slabs have grown larger. They will be biggest on the leeward sides of ridges where the wind has drifted new snow and stiffened it at the surface. They can entrain large amounts of debris that piles up deeply. Avoid slopes steeper than about 30 degrees.

    (2/4/2021) Thursday afternoon, falling cornice chunks triggered slabs on the slopes below.

Avalanche Discussion

The forecast region has seen a spate of large and very large natural, human- and remotely triggered avalanches over the past week. People have reported near misses, and at least one person was caught, carried and slightly injured. These slides have occurred nearly every day, not just during storms. They have been breaking very wide and running fast and far down slope. It's clear that weak layers that formed in late January have been at their tipping point for days.

This hazard is growing even more serious as a potent storm lashes our area. As the day progressed on Thursday, natural, explosive triggered, and human-triggered avalanches grew larger and failed at the new/old interface, and on deeper buried weak layers. With more snow and winds today, the hazard will grow more widespread.

Since midday Thursday, the Noisy Basin SNOTEL has recorded 1.6" of new water. It may receive at least half again that much by midday Friday. The Flattop Mountain SNOTEL picked up 0.7" of new water and may get another 0.6" during the same time period. In the Whitefish Range, Stahl Peak reports 0.5" of snow water equivalent. These Snow Water Equivalents amount to 5-15 inches of new snow.  Westerly winds made slabs larger below leeward ridgelines.

Buried surface hoar and facets are widespread at middle and upper elevations across the region. They lie under soft slabs of recent and drifted snow atop the stout mid-January crust. Slabs are bigger, and thus, the stress on weak layers is greater, as you gain elevation into terrain where winds have drifted new and recent snow. That structure -  bed surface, sensitive weak layer, slab - is the recipe you learned about in any avalanche education you may have had. There is a lot of new loose snow at the surface, and avalanches will entrain large amounts of debris as they speed down the hill. The hazards are not limited to starting zones. Avalanches can run down to lower elevations.

Regions covered