Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Below freezing temperatures will help refreeze the snow surface and reduce the likelihood of natural and human triggered avalanches. Massive natural avalanches failed the past two days on south and west aspects at upper elevations. Debris from one crossed a foot trail far below the current snowline. Once temperatures begin to rise later in the day, take cover and avoid traveling below large avalanche paths that are getting hit by the sun. 

Lawinenprobleme

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3.5

    Natural avalanches large enough to destroy a house released the past two consecutive days. Debris ran long distances and traveled well below the current snowline.  Meltwater making its way through the snowpack has transitioned the problem from persistent slab to wet slab.  An overnight refreeze will help lower the likelihood of the problem, but not eliminate it. If you feel a surface crust soften and break down, be cautious around steep slopes, especially ones that face south and west. If triggered, slides will run far distances while taking out the entire season’s snowpack below. Avoid traveling below steep, sun-exposed slopes later in the day. 

    (3/28/2022)

    Debris from a very large natural avalanche on Stanton Mountain in Glacier National Park. The debris ran nearly to Lake McDonald. The avalanche occurred Sunday afternoon.

    Photo: Cam Johnson

  • Cornices

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

    Large cornice failures occurred this past weekend. If traveling ridgelines, give the leeward edges a wide margin for error since cornices can break further back than expected. Move quickly, or avoid traveling below heavily-corniced slopes. Cornice failures will be more likely later in the day with incoming solar radiation and warming temperatures. 

    (3/28/2022)

    Warm temperatures have weakened cornices. This one in John F. Stevens Canyon failed Sunday, 3/27. The debris ran over 1000 vertical feet and entrained wet snow as it descended.

    Photo: Adam Clark/BNSF

Avalanche Discussion

I am happy to say that a cooling trend is occurring. Overnight low temperatures at most weather stations above 6000 feet are between 25 and 30 degrees Fahrenheit. The one exception is Noisy Basin in the Swan Range, which is still above freezing. Temperatures continue to drop this morning, bringing freezing levels down to roughly 4000 feet. They do climb again this evening and again tomorrow. After Wednesday, we should be in for a sustained period of cold overnight temperatures.

This morning you should feel a hard and supportable crust under your foot or machine. While the crust remains intact, it will reduce the likelihood of triggering an avalanche. Your turnaround sign is a softening surface crust. Continue to steer away from and avoid walking beneath corniced ridgelines since those can fail at any given time. The destructive force of recent slides should make you steer away from avalanche terrain on south and west facing slopes if/when the surface crust breaks down. It won’t hurt to have a more conservative approach today given how recent slides failed.

You will notice we dropped Loose Wet from the avalanche problem list. This is due to temperatures dropping below freezing and that surfaces are worked over from a week of warm temperatures. A refrozen surface this morning should buy us enough time today to reduce the likelihood of loose wet avalanches. We are more concerned about meltwater making its way further down in the snowpack causing destructive wet slab avalanches. This problem is possible on south and westerly slopes where a thinner snowpack exists and where meltwater is reaching buried weak layers. Overhead hazard later in the day is the biggest threat for these monsters. 

The extended weather outlook looks like a spring diurnal freeze/thaw cycle is on tap. If this forecast verifies, I’d anticipate a dropping danger and a window for steeper/bigger objectives. Time and cooler temperatures will tell.

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