Lawinenlagebericht

Snoqualmie Pass

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You can trigger a slab avalanche on recently wind-loaded terrain features partially obscured by shallow fresh snow. Slabs may overly a weak interface, allowing small avalanches to propagate farther and faster than you expect. Travel with an awareness for consequential terrain below, such as cliffs or terrain traps.

Lawinenprobleme

  • Wind Slabs

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

    Strong easterly winds Tuesday night formed fresh slabs on lee sides of exposed features, near and above treeline. Wind deposited snow primarily on atypical SW-NW-NE aspects. Slabs are 24-48 hours old and slower to heal given the cold temperatures. Look for slabs in the lee of ridges, but also on cross-loaded sub-ridges well below ridge crests. Slabs may develop over a weak snow interface causing them to trigger more easily, propagate widely, and run quickly.  Several additions of shallow, less wind-affected snow (2-3" total) likely cover the tell-tale signs of the recently formed slabs making them difficult to identify.  Look for small sharp cornices protruding from the low-density snow at the surface. Use your pole or probe to check for firmer or punchier layers just below the surface. Even though we think these potential avalanches should remain small, they can still harm you on steep slopes above cliffs, gullies, rocks, or trees.

    (12/22/2020) Example: A small wind slab in a confined terrain feature. Similar slides are possible Thursday

Avalanche Discussion

The upper snowpack continues to grow incrementally, gradually improving the riding conditions. Another 1-2" of snow is expected Wednesday night into Thursday, falling on top of 2-3" that fell late Tuesday night into Wednesday morning. Although the Alpental upper station anemometer is not reporting accurately, strong E winds were confirmed by Alpental Pro Patrol Tuesday and Tuesday evening, transporting low-density snow at all elevations. On Sunday (1/24) through Sunday night, 4" of snow likely buried a combination of facets, surface hoar, and a very thin sun crust. Each small storm continues to grow the upper snowpack. On open slopes, you could find 7-12” of snow over a very prominent and sometimes icy crust (1/13), limiting avalanche activity to the upper snowpack.

By Thursday, expect 5-8” of snow to cover the potentially weak (1/24) interface.  A slab is necessary for avalanches on this interface. Winds late Tuesday provided a critical ingredient of slab formation, but Alpental Pro Patrol found that the low-density snow has tended to remain less cohesive than one would expect given the strength of the winds. This interface may be difficult to identify if you don't find a slab above the layer.

Outside of wind-affected areas, expect unconsolidated snow poorly bonded to a very firm crust. You may trigger small loose dry or sluff avalanches on slopes greater than 40 degrees. Don’t let these slides catch you off guard if you travel in higher consequence terrain such as above an open creek or cliff. 

While travel conditions continue to improve with the new snow, you may still encounter icy slopes. Expect firm or icy conditions beneath thick trees and along wind-scoured ridgelines. This observation from Tuesday highlights these potential challenges. 

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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