Lawinenlagebericht

West Slopes Central

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 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Slab avalanches continue to pose a threat in wind exposed terrain. Identify and evaluate features you suspect hold wind drifted snow before committing to steeper slopes.  Anticipate higher danger if you find more snow and stronger winds than expected.

Lawinenprobleme

  • Wind Slabs

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

    Light snowfall and moderate winds could build another round of fresh wind slabs. The size and distribution of these are dependent on how much new snow falls over the course of the day. In addition to new wind slabs, you can trigger older slabs, some of which formed over buried surface hoar.  One remotely triggered avalanche was reported on Tuesday from northerly, near treeline terrain. Though intact surface hoar layers are spotty in distribution, they exist in some areas and could be the weak layer in slab avalanches in the coming days. 

    Actively drifting snow and other visual clues should show you where fresh wind slabs lie in wait just below ridgeline on steep, leeward slopes. Poor visibility could make wind slabs harder to pick out in the terrain around you. Monitor new snow depth as you gain elevation and change aspects. Use simple tests like hand shears and test slopes to see how well wind slabs are bonded to layers below - or simply bypass steep wind loaded slopes on lower angle, planar terrain. Assessing a deeper layer of surface hoar often requires pits and snowpack testing. 

     

     

    Example of cracking on a wind loaded test slope.

    Photo: Dallas Glass

Avalanche Discussion

You may also encounter signs of instability like rollerballs and small wet loose avalanches from light rain or during sun breaks, especially with more than a few inches of new snow. Pay attention to changing conditions and remember avalanche danger can quickly increase during periods of intense snowfall or rapid warming.

On Wednesday observers in West North triggered shallow, D1 slabs in terrain steeper than 40 degrees. It’s likely that a period of warming in the morning increased slab reactivity, even on northerly terrain. Small wet loose avalanches were observed on most aspects before skies clouded over in the afternoon. Clouds filled in earlier in the day and produced much less wet avalanche activity in Snoqualmie and Stevens Passes. Expect to find a crust on temperature and sun affected snow surfaces. Extensive wind transport was noted on the higher peaks around the North Cascades with less below 5500'.

A large avalanche was reported from the north aspect of Table Mt. in the Baker Backcountry. It was naturally triggered during the latest storm and is suspected of releasing in buried surface hoar based on how widely it propagated (crown width measured with mapping software at +600’). On Tuesday a much smaller avalanche was remotely triggered in buried surface hoar at a similar aspect and elevation. Observers actively looking for surface hoar in similar terrain found none on Wednesday. If you were to find buried surface hoar, it would be on northerly, mid and upper elevation slopes where it managed to survive sun, warmer temperatures, and wind. In a snowpit you would find surface hoar below the most recent snow but above a melt-freeze crust from early April. Remember that avalanches that fail in surface hoar layers can release above you, when you are in the middle of the slope or surprise you when you least expect it.

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