Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Fri
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You may be able to trigger avalanches up to 2 feet thick, especially where the wind has drifted snow. Loose snow avalanches will release on very steep slopes that face the sun. 

Problemas de aludes

  • Persistent Slabs

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

    You could trigger a persistent slab avalanche on shady slopes (NW-N-NE-E) at middle and upper elevations. Tuesday's storm added weight to the weak layers responsible for last week's avalanche cycle (observation and photos here). It's hard to predict whether the recent and windblown snow will be enough of a load to "wake up" these weak layers. However, we can say that this problem is likely to be at its worst on shadier aspects where the wind has stiffened the snow surface or formed drifts.

    Persistent slab avalanches can behave in ways that surprise you, wrapping around small terrain features and releasing well below obviously wind-loaded terrain. Small changes in aspect or elevation can have a big impact on stability. Slow it down and choose more conservative terrain where this problem is expected to exist. 

    ADDITIONAL DISCUSSIONA professional did not encounter wind slabs near Copper Mountain yesterday. Banner Summit can sometimes escape a storm with little wind affect. Certainly less than the taller mountains to the south. That said, I'd keep a lookout for fresh wind slabs in the alpine. Yesterday in the Smoky Mountains, I found small wind slabs up to 1' thick (photo). Similar drifts were reported in the Smiley Ck drainage (photo).

    Wind slabs often form near or just below ridgelines and on the sides of cross-loaded gullies. Many of them rest on slick crusts. This means they may be easy to trigger and will pick up speed quickly as they travel downslope. While the wind slabs may or may not be big enough to bury people, they could be powerful enough to carry you downslope or trigger the persistent slabs described above.

    (3/2/2022) This series of persistent slabs failed near the tail end of the warm, wet storm last week. These crowns span over 1,000' of NE/E-facing slopes around 8,400-8,700'. 

  • Loose Dry

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Certain
    Tamaño
    1–1.5

    The sun will initiate loose snow avalanches on very steep slopes. Avalanche activity will start on E-facing slopes this morning, follow the sun as it moves through the southern sky, and end on W-facing slopes in the afternoon. These slides commonly initiate near warm rocks, fanning out and collecting snow as they go. Human triggered loose snow avalanches (or sluffs) are also possible on very steep, shadier slopes that are sheltered from the wind.

    Although likely to be small, sun-induced avalanches will be numerous and can travel quickly on the slick surfaces beneath them. Pay attention to the terrain above you. Large slopes can produce slides big enough to knock you off of your feet and carry you places you don't want to go. 

Avalanche Discussion

Tuesday's storm and the subsequent arrival of frigid arctic air have it feeling very "wintery" out there. However, the winter feel is not relegated to just the weather, the upper 1-2' of the snowpack is looking "wintery" as well. Weak layers including multiple crusts, layers of facets, and surface hoar lie beneath the recently fallen snow. The composition of these layers is highly variable and depend on aspect, elevation, slope angle, and the amount of recent snowfall. 

As a quick example, you can see the contrast between this S-facing pit and this N-facing pit I dug yesterday in the Smokys. These pits were less than a 1/4 mile from each other and at similar elevations. The point here is that it's complex. Not only do the weak layers change, but the thickness and stiffness of the slab vary as well. In some areas, you'll be scratching around in "dust on crust". Around the corner, you could run into a stiffer, sensitive drift.

Keep these potential weak layers in mind today. No matter where you head, you're most likely to trigger a slab avalanche where you find stiff, recently formed slabs. With increased complexity comes increased uncertainty. To deal with this, SAC forecasters are beginning to avoid large or high-consequence starting zones over 35* where these weak layers might exist. 

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