Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

Tue
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 very dense, 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 large avalanche you trigger. Avalanches can be triggered from long distances away from where the slide releases and can break much wider than you might expect. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    What is it? Multiple parties triggered avalanches in the past two days. 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 more new snow continues to delay the healing process of weak layers. 

    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. Last week, widespread avalanche activity was observed on 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. 

    (3/12/2023) This avalanche failed on a SE slope at 9000' in Lola Creek. Based on the aspect and the appearance of the crown, this slide likely failed on a layer of facets below a melt freeze crust.

Avalanche Discussion

When looking at a calendar, spring might be right on the doorstep, but today's snowfall is a reminder that winter is holding on tight. The new snow is unlikely to cause the same extraordinary avalanche cycle witnessed last week. It is slowing the healing process of the weak snow that formed during the January and early February drought. We find ourselves in a stalemate position, where a continued load isn't changing the sensitivity of triggering avalanches. 

Typically as we move away from large loading events, the likelihood of triggering slides decreases. That is not the case with more snow in the forecast. The Western Smoky & Sawtooth Mtns and Sawtooths are expected to receive the bulk of today's snowfall. Stay conservative with your terrain choices for the day. Here is a rundown of what to expect in the mountains:

  • Shady slopes facing NW-N-NE-E have a stack of faceted snow that developed during the extended mid-winter 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 and additional snow and wind loading events, eventually detaching from the ridges they cling to. Cornices that fail can effectively trigger the weak layers described above in the persistent slab problem.  A group yesterday proved that this is possible (observation). 
  • If the sun makes an appearance in between passing snow showers,  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. Have a conservative plan for entering the backcountry and stick to it. 

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