Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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

In sintesi

Triggering a large avalanche involving 2-5 foot thick slabs of snow is possible on many slopes. You are unlikely to get direct feedback that the snowpack is unstable; the first sign of instability may be the very large avalanche you trigger. Avalanches can be triggered from long distances from where the slide releases and can break much wider than expected. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    What is it? Dense 2-5 foot thick slabs are sitting over weak, sugary facets and/or crusts that remain sensitive to your weight. This structure caused over 300 recorded avalanches large enough to bury a person (map, list). The snowpack is slowly adjusting to last week's massive thump of snow and wind, and our expectations of riding in bigger terrain should also reflect that we adjust to that timeline. 

    Where is it? The sensitivity and size of the avalanche vary from slope to slope (see the Forecast Discussion). The problem increases the higher up you travel from the trailhead. While springtime conditions may exist near the valley floor, a winter snowpack still clings below the recent snowfall. Widespread avalanche activity was observed in all aspects and elevations.

    How can you recognize it? The countless number of avalanches can direct your attention to slopes capable of causing similar slides. These avalanches serve as a reminder of the terrain and the consequences of causing a destructive avalanche. Collapsing, cracking, and poor results from stability tests go down in frequency as the weak layer gets buried deeper in the snowpack. Triggering a large avalanche might be the first sign of instability you receive. 

    How can you manage it? Avalanches can be triggered from well above you on the slope you are riding or skiing. Tracks on a slope are not an indicator of stability. The slope might withstand the first, second, or even last person on it before producing a devastating slide. 

    ADDITIONAL DISCUSSION: If you head into upper elevation terrain, you may find some recent, smaller wind slabs at the surface. Compared to the persistent slab problem described above, these "simple" wind slabs are much less hazardous. However, they will be large enough to knock you off your feet and send you downslope. Wind slab avalanches that you trigger can be effective triggers for the deeper weak layers that lay beneath. Large cornices that fail can also be "great" triggers for these weak layers. Yesterday a group on Galena Peak could cut a large portion of a cornice off and trigger a large avalanche (observation). 

    (3/16/2023) This very wide avalanche was observed in West Beaver Cr, near Smiley Creek at 8,200-8,800'. The crown is an estimated 3,500' (2/3 of a mile) wide.

Avalanche Discussion

We are only four days from when AVALANCHE WARNINGS and HIGH avalanche danger was across our forecast area. Very large avalanches (those big enough to destroy your house) were failing naturally just four days ago. That information alone should be enough to point you toward conservative terrain today. The persistent slab problem described above is our primary concern today. Here are a few other things to think about as you travel:

  • Shady slopes facing NW-N-NE-E have a stack of faceted snow that developed during the extended January and early February drought.  A thicker slab overlays this layer in areas that have received more wind-affect and higher snow totals.  A dense slab makes triggering the weak layer lurking below more difficult. If you do end up triggering this layer, it will likely propagate around terrain features and become an unsurvivable avalanche. These sleeping giants are trying to rest after two large storm cycles - don’t wake them up.
  • Sunny slopes facing SW-S-SE-W have a thinner slab sitting on top of a melt-freeze crust.  Since these slabs are usually closer to the surface than their north-facing counterparts, it's going to be easier to trigger these slides. 
  • Cornices have grown to monstrous sizes in recent weeks. These beasts sag and deform during warm temperatures, eventually detaching from the ridges they cling to. Cornices that fail can effectively trigger the weak layers described in the persistent slab problem above.  A group yesterday proved that this is possible.
  • If the sun makes an appearance,  pay attention to if the snow is becoming mussy or if slopes above you have roller balls coming down. This time of year, the sun doesn't have to be out for too long to warm up the snow. These wet slides can also be effective triggers for persistent slabs.

The important take-home message is most of these avalanches will be big enough to bury you. Depending on the aspect, some will be very large avalanches that are unsurvivable.  While stability is gradually improving and the likelihood of triggering large avalanches is gradually decreasing, the consequences remain the same. Have a conservative plan for entering the backcountry and stick to it. 

Check out the Weekend Update, where Ben talks more about the current conditions. 

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