Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

A third day of above-freezing temperatures and sunshine will create complex and dangerous avalanche conditions today. The risk will be highest late in the day. Avoid being on or under steep slopes that are receiving direct sun or are capped with overhanging cornices. 

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2.5

    Large natural and triggered wet snow avalanches are likely on slopes steeper than about 38 degrees where the snow surface isn't refrozen. Be off of and out from under steep slopes early. On slopes where the surface snow is getting wet for the first time, balls of wet snow rolling downslope are clear signs that conditions are getting dangerous. 

    (3/5/2022)

    Large wet loose avalanches like this one pose a hazard today.

    Photo: Brian Merewitz

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–3

    Sustained warm weather has increased the likelihood of slabs failing on weak faceted snow buried 1 to 3 feet deep. The resulting avalanches may be very large and destructive.  Whumpfs, collapses, and shooting cracks are warnings of this hazard. Mitigate this risk by seeking slopes less than 30 degrees that are clear of convexities and terrain traps.

    (3/23/2022)

    This very large natural avalanche (HS-N-R3-D3-O) released on the afternoon of March 23. It may have been triggered by cornice fall. The slab intially released on a near-surface weak layer, then stepped down to a more deeply buried layer. The avalanche occurred on an east-facing, upper elevation slope on Mt. Cameahwait.

    Photo: Adam Clark

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Cornices are weakening and sagging in the continued warm temperatures. They can break and trundle large amounts of very hard debris down slopes below them. This debris can also trigger larger avalanches on deeply buried weak layers. Don't linger under looming cornices. Stick to the windward sides of ridges, well back from cornice edges.

    (12/5/2021)

    Cornices overhanging shady slopes can pose a hazard of their own, or can triger slides that break on deeply buried weak layers. 

    Photo: Dundas

Avalanche Discussion

The cold front forecast for this morning is working its way across the region. Air temperatures have dipped or will dip below freezing above about 6000 feet before they rebound into the upper thirties. Skies are forecast to be be partly cloudy much of the day. The combination of above-freezing air temperatures and sustained sunshine drives today's avalanche hazards. No supply chain issues with water production at the snowpack surface today.

We're starting to see the classic effects of a sustained warming period: long-running wet loose avalanches, small wet slab avalanches, cornice fall, and large or very large natural avalanches breaking deep in the snowpack. I expect more of the same today. Because of the stout crusts left by this winter's various rain events, I don't see most wet loose avalanches gouging deep below the snow surface and entraining destructive amounts of debris. Meltwater percolating into near-surface weak layers could result in D1 to D2 wet slab avalanches in southerly, mid-elevation terrain. On isolated slopes, cornice falls could trigger very large slabs that break on deeply buried weak layers, as was reported Wednesday in an open, upper-elevation bowl in the Flathead Range. 

So conditions are complex, with most terrain exposed to more than one avalanche hazard, often from steep slopes well overhead. There's plenty of uncertainty associated with some of those hazards, particularly the Persistent Slab problem. And travel conditions won't be easy. How to safely enjoy Springtime sunshine in the mountains? Reduce your exposure by limiting your travel to avoid being on or under steep slopes during periods of sustained sunshine and warm temperatures. In terrain where the surface snow remains cold and dry, stick to planar slopes less than 35 degrees that have clean runouts. Assume slides could run surprisingly far and regroup in areas well outside the runouts of start zones above you. 

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