Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

Human triggered avalanches in the storm snow layers are likely. These weaknesses could be buried 1-2+ feet deep. Avoid slopes steeper than 35 degrees, and travel quickly and carefully through runouts beneath large avalanche paths. 

Problemi valanghivi

  • Storm Slabs

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

    Observers reported touchy conditions in the last four days, with several natural and human triggered avalanches up to destructive size 2. Avalanches broke mainly on the most recent new/old snow interface one to two feet beneath the surface. More snow since then could mean that the interface is buried even deeper. Wind is peaking Tuesday night and there is a short break from precipitation on Wednesday. This lull will help conditions settle for a quick period.

    The snow that fell in the last 2 days was heavier than snow that fell at the beginning of the weekend. This causes an “upside down” snowpack, where the heavier snow is sitting over a lighter layer. These conditions are oftentimes alarming, as avalanches usually fail easily on the light snow, with the denser snow acting as a slab on top. Stay alert for this as you travel by noticing thicker surface snow which then punches down to the lighter underlying layer. This upside down snowpack is present and reactive throughout the zone, but it is most concerning on leeward slopes at upper elevations where wind may have deposited snow into thicker slabs.  Avoid slopes steeper than 35 degrees at this time, especially ones with signs of wind loading, and consider traveling around the runouts of large steep slopes as well. 

    (2/13/2021) Skier triggered avalanche (D1) that broke 8in deep on the old/new snow interface on a N aspect at 4900ft near Austin Pass. Photo: Pete Durr, USFS Backcountry Ranger

  • Deep Persistent Slabs

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

    The mid January deep persistent layer is getting buried deeper making it more difficult to trigger, and observers are also noting it strengthening. The last reported avalanche that failed on this layer was February 3. Despite this information, don’t forget about it yet. An avalanche failing on this layer is unlikely, but even the smallest possibility is alarming. Uncertainty remains, and this weakness presents a very serious low likelihood/high consequence scenario. If you are in an avalanche which failed on this deep slab you would probably not survive. 

    Large triggers like cornice fall or motorized users have the best chance at affecting such a deeply buried weak layer. Continue to build in a wide margin for error and approach steep open slopes above 4500ft with a cautious mindset. Utilize good travel practices like riding one at a time and keeping eyes on your partners. If you must travel near or below steep upper elevation slopes, your best options are areas where avalanches on this layer already occurred.

    (2/3/2021) A person touring along the ridgeline from Artist Point to Huntoon Point remotely triggered a cornice that fell onto the slope below triggering this large avalanche. The avalanche occurred on a NE aspect at 5000ft and failed about 1 meter deep on the 1/24 interface.

Avalanche Discussion

Keep an eye out for moistening snow surfaces and wet loose avalanches on sunny slopes as there is a good chance we’ll see the sun. These are most likely to happen in steep areas with rock bands or near trees, where a tree bomb could start an avalanche. If snow starts getting wet and heavy, retreat to shady aspects.  

A few close calls with avalanches occurred in the last few days.  One involved two skiers on a SE aspect at 4600ft near Herman Saddle on Sunday. Both skiers were caught and carried by the avalanche but they remained on the surface of the debris and were uninjured. The avalanche was estimated to be 6-12in deep, 200ft wide and ran 50 vertical feet (observation). 

Non-avalanche hazards also exist at this time including tree well and deep snow immersion. Find out more information about deep snow safety HERE.

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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