Lawinenlagebericht

Snoqualmie Pass

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Forecast updated 0720 due to higher than expected snowfall amounts and strong easterly winds resulting in dangerous conditions at all elevations. Any avalanche risks disturbing deep persistent instabilities that are much less predictable. Large open slopes deserve a wide birth as they may produce very large avalanches.

Lawinenprobleme

  • Storm Slabs

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

    Dangerous storm slabs will build throughout the day on Saturday with around 10" of storm snow expected through Saturday. Moderate to strong easterly winds will also continue to drift the snow onto atypical aspects. You are most likely to trigger a slab on a wind-loaded slope or convex rollover steeper than 35 degrees where you find 8" or more of new snow.  There are plenty of potential failure planes in the snowpack at present. Storm slabs may sit above recently formed wind slabs and above potentially weak snow layers. A weak interface may allow slabs to trigger easily and propagate widely. Any human-triggered avalanche risks awakening a deep slab avalanche.

    Example: Storm slab.

  • Deep Persistent Slabs

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

    Over the past week natural, human triggered, and explosive triggered avalanches will not let us forget about a deep persistent weak layer. Until Thursday, we were getting fresh reports of avalanches on this layer each day and the new snow loading Friday night and Saturday may wake these layers back up. In recent avalanche incidents, riders have reported feeling lulled into a false sense of security due to a lack of observable avalanche activity in the local terrain. Recognize this cognitive trap, come up with a safe travel plan, and stick to it. The recent red-flag avalanche observations implore you to continue to give this tricky avalanche problem the respect it deserves. Several persistent weak layers exist in the snowpack. If you trigger any of them, it would result in a very large and destructive avalanche. Avoid traveling on large open start zones, particularly at mid-elevations.

    (2/9/2021) Natural deep persistent slab release on February 9th, a few days after any snowfall. South Cabin off Big Chief.

Avalanche Discussion

Easterly winds on Thursday drifted snow into new and reactive wind slabs that were particularly prevalent on atypical westerly aspects.

Another dose of snow and increasing easterly winds Friday night and Saturday will increase the risk of triggering avalanches. While you’re most likely to encounter the newly formed storm slabs, it’s the deeper persistent layers that weigh heavily on our minds. It's very difficult to predict when additional snow or wind loading will tip the balances of this classic low-likelihood high-consequence scenario. Continue to let the dire consequences shape your terrain selection. 

If you dig in the snow you may find two significant weak layers. A thin facet/crust (2/1) combination sits 3-4’ below the snow surface. Slightly deeper (4-5') the more widespread and easier to identify mid-January crust/facet layer exists. This layer failed in several recent avalanches including a very large natural in the Denny Creek drainage on Wednesday, a near-miss near Stevens Pass, a burial just east of Snoqualmie Pass, and an avalanche fatality near Salmon La Sac (See the short video in the media gallery below for more information). The snowpack structure appears nearly identical in all of these events. You can help us track this weak layer by submitting snowpack observations on our public site. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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