Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

We have issued an Avalanche Watch for the forecast area. Dangerous avalanche conditions may develop in the next 24 hours as a powerful storm impacts Northwest Montana.

Until late afternoon, keep safe by tracking new snowfall and wind loading. Avoid slopes steeper than 35 degrees where you see shooting cracks, or 8 or more inches of dense snow on top of softer snow. Steady southwest wind, increasing snowfall, and rising temperatures will cause the avalanche danger to rise quickly by evening and into tomorrow. This is not the day to start your overnight trip.

Lawinenprobleme

  • Storm Slabs

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

    Snow showers Saturday morning will increase in intensity by midday. Temperatures will rise from the single digits into the 20s. Wind speeds will be steady, and strong enough to blow snow onto leeward terrain. Those three factors will make the top of the snowpack upside-down, with a stiffer slab over weaker, unconsolidated snow. Use small test slopes to look for shooting cracks. Plan to dial back your terrain choices by the time slabs grow to 8 inches or thicker. In areas where wind slabs formed over the past few days, new snow may mask their texture and rounded shape making them harder to identify. A simple way to avoid the problem is to avoid exposure to slopes steeper than 35 degrees.

    (12/17/2021)

    The crown of a thin storm slab failed at low elevations during our last storm.

    Photo: Dundas

  • Loose Dry

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

    Bushwhackers in the Middle Fork noted natural sluffs of loose snow on Friday. As more snow falls onto an incohesive snow surface, avoid overhead exposure to very steep slopes. As you travel through wind-sheltered terrain, avoid confined chutes where you cannot escape moving snow. Avoid slopes steeper than about 40 degrees above terrain traps.

    (12/15/2021)

    Sluffs tumbled easily down very steep slopes, but only took the top few inches of the snowpack with them

    Photo: Nelson

Avalanche Discussion

Changes are coming by nightfall. Depending on the timing of an incoming, powerful winter storm, you may find MODERATE avalanche danger on Saturday. The weather will deteriorate after midday with snowfall becoming moderate, then heavy. Temperatures rise as the precipitation increases. Winds will be at snow-blowing speeds and increase out of the southwest overnight before doing a 180 with another Arctic intrusion Sunday morning.

A group attempting to ski the Middle Fork on Friday noted a lot of bush. Moreover, they noted natural loose dry avalanches in very steep terrain. Skiers in the Apgars got propagating test results under recently formed wind slabs in their snow pit. Skiers in Southern Glacier Park triggered small wind slabs on easterly slopes near and above tree line on Thursday (Example 1, Example 2). Small avalanches broke from a skier’s feet in the Northern Whitefish Range on Wednesday.

The snowpack, overall, is right-side up. Column tests have mostly failed within the recent snow. Snow depths above about 6,000 feet range from 2 to 6+ feet. The snowpack has a similar structure, but is thinner on typically sunny and windward aspects. A thin layer of rounding facets rests atop the hard basal crust buried in early December. We’ve had few reports of stability tests failing on this buried weak layer, except for propagating ECTs in the Apgar Range. Where fresh slabs form on south- and west-facing slopes, these small weak grains may be closer to the surface.

Check out the new Conditions Blog tab for a great summary of conditions leading up to the big storm.

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