Lawinenlagebericht

West Slopes North

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Expect dangerous avalanche conditions with a sharp rise in snow levels and steady precipitation. Travel with a conservative mindset and keep tabs on changing snowpack and weather factors throughout the day.

Lawinenprobleme

  • Storm Slabs

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

    Another round of snowfall will build new storm slabs even as the current crop becomes dormant. Forecasted snow amounts and wind speeds alone would be enough to see some avalanches on Monday. An additional factor is a sharp rise in snow levels that could create prominent strong over weak layering as heavy, wet snow falls on colder and drier snow below. Note changes in texture, depth, and layering for the whole of the day - not just when you first get on the snow. Approach steeper terrain features with caution and plan on scaling back to simpler, lower angle, as the storm slabs become touchy and easy to trigger. If there is more snow than forecast and you start seeing widespread human triggered and even natural avalanche activity, assume a higher level of danger and simply avoid avalanche terrain. As usual, you are more likely to trigger an avalanche in areas of recent wind loading.

    (3/19/2022)

    Natural storm slab avalanche at Austin Pass.  D1.5 on a northwest aspect @ 4600'.

    Photo: Lee Lazzara

  • Loose Wet

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

    Expect wet avalanche activity with a transition from snow to rain in the afternoon. Rain on a cold and dry snowpack like we currently have is a favored recipe for wet loose avalanches. If the rain comes sooner or there is more than forecast wet slab avalanches are possible as well. When you start seeing signs of instability like rollerballs, pinwheels, and very small wet loose avalanches it’s time to reign it in as wet avalanches will likely grow in size and frequency. Move off and away from steep slopes when you observe the beginnings of wet avalanche activity and pay particular attention to terrain overhead. Don’t get committed to places that could be difficult to escape if conditions change suddenly.

    Wet looose avalanches in the Baker Backcountry earlier in the winter

    Photo: Alyssa Young

  • Deep Persistent Slabs

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

    Three very large (D3) avalanches were reported on Wednesday around Baker - two naturals and one from avalanche control work. Observations since the last storm are sparse due to poor visibility - we can’t say either way if more avalanches of the same character did or didn’t occur with Saturday’s storm.  

    The reported avalanches likely released in a layer of weak facets buried on March 8th. As the layer in question gets buried deeper, triggering one of these avalanches is more difficult. With the end of heavy snowfall, it's less likely one will release naturally - but it could still happen. A large load like a cornice fall, smaller avalanche initiating in higher terrain, or a group of people on a slope could trigger one where a single person might not. This isn’t really a “manageable” avalanche problem that can be figured out and mitigated with snowpits and other assessment tools. You are either in the terrain where it could happen or you are not. If you chose to travel these areas you are simply accepting a slightly higher risk of triggering or being overrun by a very large avalanche. 

Avalanche Discussion

Observers in Canyon Creek and Baker BC found much improved stability compared to Saturday with no new avalanches reported. It was still possible to get deep cracking in storm slab layers on unsupported slopes but the slabs were too well bonded below. Light density new snow overnight had begun to fill in the many crowns from the avalanche cycle on Saturday and strengthening winds in the afternoon had begun to transport snow and finish smoothing things out. Observers on the west side Table Mountain saw no new deep slab avalanches in alpine terrain. Though a single observation in one drainage does not cancel out the deep persistent avalanche problem, it is the first sign that the big avalanches last week may have been one-off events. 

Satruday's storm delivered more snow than expected in a very short period of time. Avalanche danger exceeded the forecast across West North - especially in the period from sunrise to about noon. Heather Meadows picked up about 1.5” of precipitation in 12 hours with other areas like Schriebers seeing similar accumulations (and avalanche activity). Snow doesn’t like rapid change - if it gets too warm or too much load too quickly it acts out. Despite limited visibility through the morning, many of the observed avalanches were impressive. They were not necessarily deep (most were 30cm or less, slightly deeper in wind loaded terrain) and the ones that could be seen were D2 in size or less. On the other hand, some propagated very wide with crowns wrapping around terrain features in ways not normally seen. Slopes that did not avalanche naturally were easy to trigger with a few kicks from lower angle terrain above. 

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