Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Fri
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Warm and sunny weather could help destabilize the snowpack and trigger a number of avalanche problems on Thursday. Very large natural avalanches have occurred recently, reminding us that the snowpack is unhappy. Don’t get lulled into poor terrain selection and decision-making just because the weather is nice.

Problemas de aludes

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    3

    We continue to be concerned about the potential for very large natural avalanches in the West South zone. Recent avalanches, warm temperatures, and a known weak snowpack structure are all red flags that should have you thinking hard about your terrain selection. For the past week, very large avalanches have occurred erratically and are suspected to have run on the Mid-January crust/facet combo. This layer’s depth will vary across the zone but has been measured close to 7 feet deep recently. Any avalanche on this layer will be very large and being caught in one would almost certainly be fatal. The timing of deep slab avalanches is difficult to predict and we could go several days without seeing another deep slab release. On the flip side, it wouldn’t surprise us one bit to see multiple happen tomorrow. Know that if you decide to enter large start zones, avalanche paths, or runout zones, that you are putting yourself at risk. Many of these slides have run very far distances and broken trees as they descend, reaching valley bottoms and areas normally considered as “safe”.

    (3/1/2021) This avalanche on Crystal Peak was heard by Crystal Mountain Patrollers on Sunday, but could not be seen. On Monday, it was discovered by a tourer and made 3 consecutive days with a very large avalanche in the Crystal Mountain Backcountry. [SE 6500'. Photo: Andrew, Public Observation]

  • Cornices

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Continued high freezing levels and sunny weather may further destabilize cornices around the zone, causing them to collapse. The largest and freshest cornices may be found on east aspects, but take a look at what’s above you regardless of what aspect you are traveling on. If a large cornice falls, it could be the trigger needed for the deep persistent slabs we are concerned about. Even if the Mid-January crust isn’t activated, slab avalanches in the upper snowpack could fail or blocks of snow from the cornice breaking could descend toward you. Cornices notoriously break further back than expected, so stay far away from them if you’re on a ridgeline. And keep off slopes that are below them.

    (2/28/2021) Winds have been strong enough in the West South recently to load leeward slopes and build large cornices. These cornices could act as triggers on the slopes below.

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Thursday will be another day of warm weather and mostly sunny skies. Without a strong overnight freeze Wednesday night, it may not take as long for the snow to soften up and Wet Loose avalanches to occur once daylight hits. Look for these avalanches on slopes that see direct sunshine and to initiate at a point such as near rocks or trees. These slides can entrain significant snow, fan-out, and even trigger slabs as they descend downhill. Lower elevations that have gone through several rounds of freezing and thawing lately could have minimal or smaller avalanches, but upper elevations could now be reaching their tipping point to produce larger slides. Rollerballs and pinwheels, the snow surface getting warm and sticky, or snow shedding from trees and rocks will be your first indicators of Wet Loose avalanches. If you notice these signs or recent avalanches with fan-shaped debris piles, head for shadier slopes keeping aware of the terrain above you.

    (2/28/2021) Pinwheels and rollerballs were observed on Sunday (2/28) in the West South and are a good indicator that wet loose avalanches are possible. [Photo: Enji Cooper]

Avalanche Discussion

We are only a few days removed from a very large natural avalanche cycle in the West South and we continue to get observations of recent avalanches that likely occurred over the weekend. The combination of continued warm and sunny weather, no overnight freeze, recent avalanches, and a known poor snowpack structure are all red flags that should give you pause. Don’t get lured into poor decision-making just because the weather is nice. Stay vigilant with your terrain selection and remember that even though a deep persistent slab avalanche may not initiate at lower elevations, they are capable of running into them.

March often brings a bit of uncertainty for forecasters as longer days, stronger sunshine, and a transition from a cold winter snowpack toward a warmer springlike snowpack happens. When the snow starts to warm up, it generally starts to fall off of things. This means that cornices may fall and trigger slabs, or blocks of snow and ice may fall off rocks and cliffs to trigger avalanches on the slopes below. Even snow falling off trees and rocks may start as a simple snowball and grow into a large avalanche as it descends. This year, we are adding a major layer of complexity to our springtime forecasting due to the deep persistent problem, giving us even more uncertainty than usual. Let this uncertainty and the consequences of these slides continue to guide your decision-making on what terrain is within your acceptable level of risk and stay safe out there.

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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