Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Wind drifted snow in alpine terrain remains a hazard. Bypass very steep terrain features like convex rolls and hanging slopes above cliffs where you could still trigger a slab avalanche. Keep an eye out for wet, unsupportable snow surfaces with rising freezing levels Tuesday morning.

Lawinenprobleme

  • Wind Slabs

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

    Deep, stubborn to trigger wind slabs blanket near and above treeline terrain, even well below ridgeline. They are difficult to identify as they are obscured by up to 1’ of new snow. Wind slabs still pose a risk to backcountry travelers on specific terrain features like unsupported rolls. These are places where slabs have little support at the downhill edge, even though the slab might be bonded to the layers beneath. 

    Stubborn wind slabs are difficult to evaluate. They generally do not react on test slopes. Hand shears are nearly impossible in the hard snow. Snowpack tests tend to produce inconclusive or simply no results - but there is still some risk of triggering the slab. On the other hand, terrain features where you might trigger a wind slab are just that - features on the slope versus the whole slope. The best way to reduce uncertainty is to simply avoid them. Use lower angle terrain to navigate around suspect, wind loaded features as you travel in the mountains on Tuesday.

    Also be on the lookout for new, shallow wind slabs on Tuesday. Moderate winds and light snowfall may drift snow onto leeward slopes at higher elevations.

    (12/20/2021)

    Wind affected snow surfaces can help identify areas of wind slab. In this photo the wind blew from right to left on 12/18. The slope off to the right was rocky and wind scoured while the slope on the left was smooth with no texture.

    Photo: Lee Lazzara

Avalanche Discussion

Freezing levels rising to 5500' and cloudy skies on Tuesday will warm the snow surface below treeline on all aspects. Expect to see numerous signs of warming snow like rollerballs, trees shedding snow, and possibly a few loose wet avalanches starting in steep rocky or treed terrain. Consider the consequences of a small avalanche near terrain traps or areas of shallow snow cover.

A widespread natural avalanche cycle occurred on Saturday sparked by 2’ of new snow, rising freezing levels, and very strong winds. Excellent visibility on Sunday allowed for observations well up into the alpine with many natural avalanches to D3 noted on all aspects. Some avalanches also ran well down into below treeline terrain as noted here. A handful of snowmobile triggered avalanches were reported the same day. The most notable came from Schriebers/Mt. Baker where a large (D2) wind slab was triggered on an east aspect at ~5000’.

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