Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
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

A natural avalanche cycle occurred in the last 24-48 hours, and human triggered avalanches are still likely.  Avalanches may fail six inches to two feet deep in storm snow layers.  Avoid slopes steeper than 35 degrees, and limit your time in areas beneath large avalanche paths as well. 

Problemi valanghivi

  • Storm Slabs

    • Tutte le quote
    Probabilità
    Likely
    Dimensione
    1–2

    Observers reported touchy conditions over the last several days, with large natural and human triggered avalanches occurring up to destructive size 2. Avalanches broke mainly on recent new/old snow interfaces between six inches and two feet beneath the surface. After a brief period of blue skies and calm, snowfall intensity and wind are increasing throughout the day on Thursday. The danger is not expected to rise by the end of the day, but make note of changing weather conditions and how it is affecting the snow. 

    The snow that fell since the weekend was heavier than snow that fell at the start of the weekend. This caused 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. Stay alert for this 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. Additionally, you will find even more touchy conditions on leeward slopes at upper elevations where wind may have deposited snow into thicker and more reactive slabs. With both of these concerns, avoid slopes steeper than 35 degrees, especially ones with signs of wind loading, and consider traveling around the runouts of large steep slopes as well.

    (2/17/2021) A snowmobile triggered avalanche at Baker Pass, 18-24” deep, approx 150’ wide. Photo: Public Observations

  • 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 finding that its strength is increasing. The last reported avalanche that failed on this layer was February 3. Despite this, keep it on your mind as you are traveling through the backcountry. 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 fails on this deep slab you would probably not survive. 

    Large triggers like cornices 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.

    An intentional cornice-triggered deep slab avalanche which probably ran on the mid January layers of concern on Feb 6.

Avalanche Discussion

On Wednesday a snowmobiler riding in the Baker Pass area triggered a large (D2) avalanche. Its depth was 18-24” and it was approximately 150’ wide. There were also numerous other avalanches seen in the area. You can read the observation HERE. Another report of unstable conditions in the Bearpaw backcountry was reported in THIS observation, where old natural avalanches were visible and a couple skier triggered avalanches occurred. 

Tree well and deep snow immersion hazards are a serious problem with all our recent snow. Find out more information about deep snow safety HERE. 

In the last week we’ve received nearly two feet of snow. Not many people got into the backcountry until our fair weather period on Wednesday, but we still heard numerous reports of avalanches failing on interfaces buried in the last week.  Additionally, wet loose avalanches occurred as the sun heated the slopes on Wednesday.  Expect to find a crust on southerly aspects as you travel out in the next few days. Our next weather system is moving in on Thursday, and avalanche conditions will remain elevated for the next several days.  

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