Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
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In sintesi

To significantly reduce the chance of triggering a large avalanche, avoid steep slopes where the wind has drifted snow, formed slabs, or stiffened the snow surface. Several natural and human-triggered avalanches occurred in this area and neighboring zones in the past three days. 

Problemi valanghivi

  • Persistent Slabs

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

    What is it?  1-3 foot thick slabs overlie persistent weak layers (sugary facets, surface hoar, and/or crusts), predominantly at middle and upper elevations. Wind-loaded slopes are the most dangerous. 

    Where is it?  Several natural and human-triggered avalanches occurred above 9000' in neighboring zones in the past 3 days.  The recent activity occurred on several aspects. Wind-exposed bowls and slopes near ridgelines, prominent gullies, and chutes are most likely to produce avalanches. 

    How can you recognize it?  Assume this problem exists until proven otherwise. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Wind-loaded areas feel stiffer under your skis or sled and keep you from easily sinking into the snowpack.         

    How can you manage it?  Unfortunately, avoiding slopes steep enough to slide is the only surefire way to manage this problem. Persistent slab avalanches are tricky. If you're playing near steep slopes, you may be able to trigger slides remotely (from gentler terrain above, below, and to the sides of steep slopes—explanatory video here). These avalanches may break wider than expected or higher on the slope above you. 

    ADDITIONAL DISCUSSION - OLD, SUGARY, FACETED SNOW NEAR THE GROUND: Faceted snow exists near the base of the snowpack. This layer has produced hundreds of avalanches this season and is buried beneath a thick,  dense slab. Impacting deeply buried weak layers with your weight is difficult in this zone, but the consequences could be severe. While not likely, it may be possible to trigger a very large slide on this layer in steep, rocky, wind-affected alpine terrain where snowpack depths are variable. Here, skiers and riders can inadvertently find spots with a thinner snowpack where triggering an avalanche is possible. Digging down to this layer with the track of your sled is another "great" way to impact this deep weak layer.

    (1/1/2023) Debris from a very large avalanche that was remotely triggered above Hyndman Creek in the Pioneer Mountains. This slide failed in a heavily wind loaded area and very likely involved a persistent weak layer. It covered the summer trail with a pile of debris that was 100-150' wide and 4' deep.

  • Wind Slabs

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

    What is it?  Recent winds formed 1-2 foot thick wind slabs in exposed terrain in much of the forecast area.Yesterday, professional observers reported two natural wind slab avalanches in the northern Sawtooth Mtns. This weekend, an experienced skier was caught and carried in a slide on Senate Peak (near Galena Summit), Ben triggered a wind slab avalanche on Galena Peak, and Chris steered clear of freshly wind-loaded slopes on Copper Mountain. 

    Where is it?  Wind slabs are largest and most widespread at upper elevations.You may find them near ridgelines, on the sides of gullies and chutes, and near prominent terrain features. Winds blowing from unusual directions (NE-E-SE) formed slabs in some places you don't normally find them.

    How can you recognize it?  Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface. Wind slabs can have a smooth, chalky appearance and feel and sound hollow, like a drum. Wind-deposited snow will be stiffer and keep your skis or snowmobile closer to the surface.       

    How can you manage it?  Given the increased chances of triggering a large persistent slab avalanche on wind-loaded slopes, the prudent move is to avoid obviously wind-loaded avalanche terrain. Any triggered wind slab could "step-down" to buried persistent weak layers (Problem 1), causing a larger destructive avalanche.  

     

    (1/1/2023) Crown of a large, 1-2' thick wind slab that was intentionally triggered on Galena Peak on a N/NW aspect at 9,500'.

Avalanche Discussion

In the past 3 days, ten avalanches occurred (view Avalanche Database here). What were the common threads?

  • All of the slides were in freshly wind-loaded or wind-affected paths, and most involved persistent weak layers buried 1-3 feet deep
  • All were above 9000' in elevation
  • Eight released in the Galena Summit & Eastern Mtns zone and two in the northern Sawtooth Mtns
  • Five slides released naturally yesterday (3 slides in the Boulder Mtns and 2 slides in the Sawtooth Mtns) 
  • Four slides were triggered remotely (from gentler terrain above or to the sides of steep slopes) over the weekend

While the danger is dropping from CONSIDERABLE to MODERATE as stability gradually improves, I'm still avoiding almost all avalanche terrain. Why?

  1. Persistent slabs: I'm not smart or experienced enough to know with certainty which avalanche paths are safe to ride or ski and which would be trouble.
  2. Risk tolerance: I'm a chicken (risk averse) when dealing with persistent weak layers. Until a persistent slab-driven avalanche danger is LOW, I will generally avoid avalanche terrain. 

You may be willing to accept more risk than me, and that's okay. While I'm not interested in riding or skiing consequential avalanche paths with a 1/20 to 1/100 chance of triggering them, many folks will take those odds and have a blast in steep terrain. I do encourage the more risk-tolerant snow enthusiasts to picture the consequences of a large avalanche before committing to skiing or riding steep slopes, especially in alpine and wind-affected, upper elevation terrain. If you're going to play in those areas, avoid places with terrain traps (cliffs, trees, creeks, lakes, or gullies) below you. If the proverbial roll of the dice comes up snake eyes and you are caught in a slide, avalanche paths with "clean", gradual runout zones provide a far better chance of simply having a bad day versus the unthinkable alternative. 

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