Bollettino valanghe

Olympics

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You are most likely to trigger an avalanche on a wind-loaded slope, including shallow slabs or potentially a very large and destructive persistent slab. We have significant uncertainty about the weak snow above the mid-January crust.  Consider reducing your exposure to large slopes steeper than 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    If the forecasted shallow snow and wind materialize, wind slabs will become dangerous above treeline by the end of the day. Focus on several inches of new snow falling and drifting with moderate W winds Friday night and Saturday. Wind slabs should be small and relatively shallow near treeline, confined to specific terrain features such as just below freshly corniced ridgelines. Above treeline, they will become slightly larger, more widespread, and difficult to steer around. Avoid slopes with active wind loading. Check the direction of fresh sharp cornices and wind lips, rime plastered on trees, and snow stripped from trees. Steer around recently wind-loaded terrain features near treeline and avoid all slopes steeper than 35 degrees above treeline.

    Example of wind-affected snow below corniced ridgelines where you are more likely to trigger a wind slab avalanche. Photo: Ethan Taylor

  • Persistent Slabs

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

    Several layers of weak snow lurk above the mid-January crusts, including facets and surface hoar. Persistent weak layers are true to their name: they persist. If you trigger one, it will propagate widely. You'll find the weak interface about 35 inches down, within the range of human trigger. Wind slab or cornice fall avalanches may be the most likely triggers on Saturday.  Any avalanche on either weak layer will be large to very large and difficult to survive. Although snowpack test results were not impressive, similar layers of rounding facets and surface hoar in the Cascades have produced numerous avalanches in recent days, some of them human-triggered. Given our uncertainty surrounding this layer, we suggest continuing to dial back your terrain selection. Reduce your exposure to large avalanche slopes 35 degrees and steeper.

    (1/30/2021) Human triggered persistent slab avalanche stepping down to 1/13 crust. Estimated to be size D1.5. North facing aspect near Victoria Overlook.

Avalanche Discussion

Thursday night's storm brought some light to moderate winds, but hardly any precipitation.  

On Thursday, NWAC and NPS professionals reported 35 inches of "right-side-up" or increasing density snow above the decomposing mid-January crust.  The observers noted a significant and widespread avalanche cycle on N aspect slopes from heavy snowfall January 31 - Feb 2.  Crowns were particularly prevalent on N-NE aspects where almost every steep, convex rollover produced an avalanche. Many were small, but some were large. Their investigation of two crowns on NE aspects at 5100 ft showed that the slide had propagated in the old snow on top of the mid-January crust.  All natural avalanche activity occurred during the storm. It is unknown whether the slides initiated on near-surface facets just above the crust or on surface hoar a few inches higher. 

Some aspects could still be close to the tipping point, but just waiting for a trigger. This uncertainty warrants increased caution and a greater margin for safety on Saturday.

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