Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Take extra precaution to avoid triggering any avalanche on a steep or wind-loaded slope. Avalanches near the snow surface increase your risk of a very large avalanche on a persistent instability. Don’t get lured onto large avalanche terrain, stick to smaller, treed, and lower angled features.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1

    Shallow wind slabs will be most reactive at upper elevations and near ridgelines where they are thicker and easier to trigger.  Slabs may run on a very light rime/facet combo layer from 2/11. If you find more than 6" of wind-loaded snow above the rime crust or old snow interface, stick to slopes less than 35 degrees. Remind yourself that any avalanche triggered risks awakening a persistent slab 2 ft or more below the snow surface.

    (2/9/2021) Example: Dry Loose avalanches start at a point and fan out as they run downhill. Don't get knocked off your feet or pushed into a terrain trap by one of these when there is so much snow. [Photo: Zack Wentz]

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Persistent weak layers are frustratingly slow to heal and we don't know how the mid-January facet/crust combination handled the new snow. Observations on Thursday documented that a weak facet/crust combination remains intact and may produce avalanches. Don’t expect obvious signs of unstable snow. 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.  If you dig in the snow, look for sugary facets above a stout mid-January crust about 2’ below the snow surface. You can use snow profiles and snowpack tests to track this layer, but don’t bet your life on a hole in the snow. The best way to avoid this sleeping beast is by staying off of large steep slopes, particularly on W-NW-N-NE-E aspects. Instead, seek out smaller, lower angled, and treed slopes.

    (2/4/2021) Persistent slab avalanche that likely failed naturally during the storm (around 2/1). Hurricane Ridge Road in the foreground.

Avalanche Discussion

Hurricane Ridge likely picked up 4-5" of snow Friday night into Saturday. This was slightly less than expected and as a result, the instabilities near the surface have likely been more limited to wind-drifted snow in the lee of ridgelines. WSW winds were in the light to moderate range Friday night. This should have been strong enough to drift the low-density snow. Temperatures have remained below 25F at Hurricane Ridge since February 7th.

Parts of the eastern Olympics may have seen significantly more snow during this storm. If you travel in areas with more than 8" of storm snow, travel conservatively at all elevations, avoiding all slopes steeper than 35 degrees. Many zones in the Cascades have reported very reactive storm instabilities, potentially running on weak interfaces.

The primary weak persistent layer we’ve been talking about for two weeks continues to sit in the snowpack. Observations from Hurricane Ridge on Thursday found small 1mm facets just above the mid-January crust on nearly all aspects. This layer failed easily in snowpack tests and showed the ability to propagate a failure across a slope. We have not received reports of an avalanche on this weak layer for some time, but that could change at any moment. You can help us track this persistent layer by submitting snowpack observations on our public site. 

While the Olympics are not the Cascades, this snowpack structure closely resembles other forecast zones across Washington. A very similar set-up resulted in several near-misses, avalanche involvements, and one fatality over the past week. (See the short video in the media gallery below for more information). If we can learn anything from these incidents, it’s that persistent slabs can be tricky and necessitate extra caution and patience. 

2020-21 Forecast Schedule: Avalanche danger ratings will be issued for the Olympics every Friday through Sunday and during mid-week holidays. During the week when the Hurricane Ridge road is closed, forecast information will be updated daily to include expected conditions and relevant travel advice under the No Rating label.

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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