Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

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

Today's primary avalanche hazards involve new and recent snow. Stick to lower angled slopes to decrease your chances of triggering a slide. Or, if you accept a higher risk of triggering slides, stick to lower consequences terrain - open slopes with easy escapes and runouts clear of things that would hurt if you hit them. Use active tests to identify where slabs exist and are reactive to the weight of you or your machine. If winds pick up sooner than forecast, expect more widespread and larger soft slabs. 

Lawinenprobleme

  • Storm Slabs

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

    Where dense snow rests on softer snow, you can trigger soft slabs that break in the new and recent snow. They may range from 6 to 24 inches thick. They can be dangerous where steep start zones funnel into confined paths or run over or into terrain traps, like rock bands, gullies, or trees. A good clue that these dense-over soft conditions is cracking around your skis, board, or machines. Active tests can help you identify where these slabs are sensitive to your weight. These tests include stomping or cutting steep, low-consequences test slopes and cornice drops. This problem is isolated at mid-elevations.

    (12/15/2021)

    Ski cuts in wind stiffened snow released shallow soft slab avalanches

    Photo: Nelson

  • Loose Dry

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

    The hazard posed by loose snow avalanches is growing more isolated as new and recent snow settles. While you might be able to trigger sluffs that run downslope from your skis, board, or machine on steep slopes, these will only be dangerous in particular terrain. Among these:  start zones 40 degrees or steeper where the track below stays continuously steep, confined chutes that leave few options to escape moving debris, and steep slopes above cliffs, trees, rocks, or gullies. Where you find loose snow over firm snow, look downslope and picture where you might wind up if you get pulled off your feet or machine. 

    (12/14/2021)

    Sluffs, like this one, are possible where cohesionless surface snow pours down steep slopes. The sluff in this picture did not entrain much snow and was harmless in size.

    Photo: Reardon

Avalanche Discussion

Wednesday's observations consistently described avalanche hazards involving new and recent snow. Clancy triggered small, soft slabs near Red Meadow Lake in the Whitefish Range, as well as a few harmless sluffs. In the northern Swan Range, skiers reported the top 6 to 8 inches of snow failed easily in small column tests. And in the Skyland area, Cam and Guy found 10-12 inches of loose, dry snow that could sluff on very steep slopes. I expect similar conditions today, with a few caveats. Always caveats. First, the recent snow is slowly settling, making for slightly more coehsive slabs and reducing the amount of snow that can sluff. Second, new snow today - 1 to 5 inches - may camouflage existing soft slabs - and resupply the loose snow avalanche machine. Third and most importantly - today's forecast assumes wind speeds will remain light until tonight. There's plenty of loose snow available for transport at the surface, so if wind speeds pick up, expect conditions to change quickly, with soft, reactive slabs of drifted snow forming rapidly.  

Several observations from Wednesday also noted potential failure planes deeper in the snowpack. These generally involved small, rounding facets near near thin crusts or density changes 40 to 100 cm below the snow surface. These generally took hard or very hard force to fail in large column tests, and didn't propagate, except in the Apgar Range. A few recent profiles have shown a thin layer of rounding facets justabove the Dec. 3 crust. This layer hasn't shown itself to be much trouble, though it's raised the eybrows of our Canadian neighbors. Before you commit to very steep, consequential slopes, do some slope-specific digging and check that your objective isn't an isolated exception to the new and recent snow avalanche hazards. 

I expect the avalanche hazard to increase overnight and into tomorrow if forecasted winds arrive. Arctic air leaks over the Continental Divide Friday, with moisture approaching from the Pacific Coast. The weekend may be stormy.

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