Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

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

Fresh snow raises the risk of small avalanches near the surface, but also low-probability high-consequence persistence slabs. Any avalanche triggered within the storm snow could act as the trigger for a deeper avalanche. Don’t get lured onto large avalanche terrain, stick to smaller, treed, and lower angled features.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    High rates of snowfall late Friday night and Saturday will produce instabilities that will be easy to trigger.  You can trigger an avalanche anywhere you find 8" of snow above the old snow interface. These slabs may fail on a very light rime layer from 2/11 or within the storm snow. Navigate around steep and unsupported slopes where you could trigger a storm slab. 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 our first major snowstorm since February 2nd may increase the risk of avalanches on these layers. Observations on Thursday continue to document that a weak facet/crust combination remains intact and may produce avalanches. Don’t expect obvious signs of unstable snow. You could walk around all day and conditions may “feel” stable. 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

The same 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.

Regioni coperte