Bulletin d’avalanche

Olympics

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Forecast danger updated 8 AM Monday due to heavy snowfall and lower than forecast snow-levels.

Don't let a relative break in the weather fool you, large avalanches will be reactive and dangerous near and above treeline. Slabs may be thicker in wind-loaded areas and could rest on weak snow at approximately 1.5-2 ft average depth. Avoid slopes steeper than 35 degrees and those connected to upper elevation start zones.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Large and reactive storm slabs formed late Friday and Saturday and by Sunday we're only 12 hours out from an expected natural avalanche cycle. These slabs are most dangerous above 5500-6000 ft where they may not sit above a crust formed by rain reaching this elevation on Friday. Another crust may form from a rain/snow line maximum Saturday evening that should be below ridgelines. Above 5500-6000 ft, you will have to worry about multiple storm interfaces, deep wind-loaded drifts, and the potential for an avalanche to occur or step down to a layer of weaker snow that produced a large human-triggered avalanche on Friday (see photo). The persistent slab nature of this avalanche keeps it on our minds, particularly at upper elevations, as we just loaded this layer further. Between 4000 and 5500 ft you are likely to find 8" or more of snow above Friday's crust, that you can trigger to form an avalanche that could be large in wind-loaded locations.  At lower elevations, you may find shallow fresh snow above a crust limiting avalanche hazard. Al these elevations, water running on rock slabs under the snowpack creates a lingering chance for glide avalanches on isolated terrain features.

    We don't know exactly where the rain/snow line from Friday afternoon/evening lies and this creates some uncertainty in our forecast near treeline. Thus, we are recommending you probe for 8" of snow above the crust as an indicator for when storm slabs are likely to become reactive. As soon as a crust approaches 8" depth, steer around slopes steeper than 35 degrees and slopes connected to large avalanche paths. If you see evidence of whumphs, collapses, or recent avalanche activity, conditions, dial back your terrain selection further.

     

    (12/31/2020) Human triggered large slab avalanche on a NE asp, 5500'. May have released on 3-4 mm surface hoar, est 1.5' below the snow surface. No one was caught or carried. Photo: Russ Hamlet.

Avalanche Discussion

Hurricane Ridge should get a break from the storm cycle on Sunday with partly cloudy and cooler weather helping to refreeze any liquid in the upper snowpack.

A series of storms brought moderate to heavy rain and snow to Hurricane Ridge Friday afternoon through Saturday.  Hurricane ridge added 13" to the snowpack since rain changed to snow on Friday. Water numbers are impressive with 1.5" of water equivalent in the last 24 hours and 3" water equivalent in the last 72 hours.  

We expect that a natural avalanche cycle occurred during the Storm cycle Saturday or Saturday evening with dry slabs at higher elevations and wet avalanches at lower elevations. 

Prior to Saturday, we've seen a few different avalanche cycles involving storm slabs 12" or less and small loose wet avalanches below 5000'.  There was one large (D2) human-triggered avalanche on Thursday (see photo above). Luckily no one was caught in the slide.  Slab avalanches may have failed on weak snow grains (3-4 mm surface hoar) now buried 12/29 and 1.5-2 ft on average below the snow surface.  We have high uncertainty regarding how widespread this layer is and whether it was wetted by rain events on Friday or late Saturday.  Below this layer, the mid and lower snowpack is strong with a series of crusts from earlier in the winter.  

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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