Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Generally stable avalanche conditions exist, and large avalanches are unlikely. Be on the lookout for fresh wind drifts at upper elevations. It would take a dose of bad luck, but there's a lingering chance of triggering a large slide on weak snow deep in the snowpack in very steep, rocky, wind-affected terrain. 

Problemi valanghivi

  • Wind Slabs

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

    A quick-hitting storm dropped 6+" of snow in this zone at the end of last week. On Saturday, on an off-duty ski day, I intentionally triggered an avalanche involving this snow (pictured at right/above). The slab that failed was 6-18" thick, up to 100' wide, and failed on a layer of weak snow (near-surface facets on a crust). The slide picked up speed quickly as it traveled downslope, eventually stopping  2,000' below where I triggered it. 

    Monday, on a recreational ski day near Banner Summit, my partners and I paid close attention to the snow surface, watching for signs of wind loading and slab stiffening and avoiding these areas where we found them. The slabs that we were avoiding did not look to be particularly large, but even small slabs of snow can do some serious damage to a soft-bodied human (all of us) in the wrong kind of terrain. Chris and his partner were nearby and they followed the same protocol. We all found better and much safer riding by avoiding these slabs. 

    If I headed out skiing or riding in this area today here are a few reasons I'd still be thinking about these drifts:

    • These slabs are sitting on a few different weak snow surfaces such as facets, crusts with facets, and surface hoar. These types of weak snow are slow to heal and can cause avalanches days to weeks after they have been buried.
    • Slabs that fail on these types of weak layers (called persistent weak layers) can do so in ways that surprise you. They may break wider than you expect and further above you than you might expect.

    Your best bet for avoiding having a problem with these slabs today is to do what my group did Monday: spend some time looking at the snow with an eye out for textures that indicate the wind has been at work (ripples on the surface of the snow, large pillowy dunes of snow, etc.). Pay attention to how the snow feels under your skis or your machine. If you are seeing signs of loading or feeling the slab stiffening, alter your course to somewhere with softer snow at the surface. You'll find better skiing and riding and much safer conditions, a real win-win.

    (1/22/2022) North winds following Thursday's 6+" of new snow created sensitive wind slabs. These are failing on weak snow surfaces that formed during the ongoing dry spell. This wind slab was intentionally triggered in alpine terrain in the Sawtooths.

Avalanche Discussion

In addition to the wind slab problem described above, here are a few other things to keep in your mind today:

  • Deep Persistent Slabs: Weak faceted snow exists near the ground on shaded middle elevation slopes and most slopes at upper elevations. In this zone, it's buried beneath a very dense, 5-7 foot thick slab. You would have to be very unlucky to trigger an avalanche involving this weak snow, but you'd need to be equally lucky to survive one if you did. I've still got this layer in mind when I'm traveling in this zone, as do many local professionals and experienced backcountry travelers. This type of slide would be most likely in steep (35+ degrees), open, rocky, wind-affected terrain.
  • Cornices:  A month of nearly continuous snow and wind in December built some truly impressive cornices. These beasts are perched along most ridgelines in this area. It can be very difficult to tell where a ridgeline stops and where the cornice starts. Give these huge chunks of snow a wide berth. Many observers (myself included) have noticed large cracks between these cornices and the ridgelines that they are attached to. In many places, these cracks are hidden by thin layers of snow covering them, a veritable booby trap. A natural or triggered cornice collapse would make a "good" trigger for the weak snow near the base of the snowpack.

Regioni coperte