Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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

In sintesi

Conditions are scary where the wind formed drifts or stiffened the snow surface. Triggering  large avalanches in areas sheltered from the wind is also possible. You could trigger avalanches remotely—from flat terrain below, above, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

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

    What and where is it: You could 1.5-4 foot thick slabs, especially where wind formed drifts or stiffened the snow surface. Triggering an avalanche is less likely—but not out of the question—on steep slopes that are completely sheltered from the wind. The slabs rest above a variety of weak layers (facets, surface hoar, crusts, and combinations). The widespread nature of the weak layers means avalanches are possible on many aspects. 

    How can you recognize it: Snowpack cracking (photo), and collapsing or whumpfing, are clear signs of unstable conditions. Watch for snow pillows, dunes, and ripples (photo), and feel for stiff snow under your feet or sled. These are signs the wind has been at work transporting snow. Assume the weak layers exist on most slopes.    

    How can you manage it: You can avoid steep, wind-loaded slopes to significantly reduce your chances of triggering an avalanche. Persistent Slabs can release in surprising ways, break wider than expected, and release above or hundreds of feet away from where they are triggered. Remotely triggering an avalanche from flat terrain near steep slopes is a real possibility. Keep a close eye on your partner and the terrain that's above you.

    (12/29/2024) This persistent slab avalanche was remotely triggered from gentle terrain above the crown. NW slope near 8600' in the Prairie Ck drainage of the Smoky Mtns. 

    Photo: Jon Preuss

  • Wind Slabs

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

    You may be able to trigger wind slab avalanches that involve only some of the snow that fell in recent days. The size and chance of triggering these slides increase significantly as you climb into windier, alpine terrain at upper elevations. These avalanches  could step down to the buried weak layers described in Problem #1 above as snow moves downslope. 

    Wind slabs often form near ridgelines and in cross-loaded areas on the sides of gullies. In the craggy Sawtooth Mtns, wind-driven snow also forms slabs in cirques and aprons below large cliff faces and couloirs. You can reduce the odds of triggering a wind slab by looking for and avoiding slopes with obvious signs of wind-loading, such as new cornice growth and large dunes or pillows of wind-blown snow.

    Additional Discussion: Several inches of low density snowfall fell near the end of the storm. Any extended periods of sunshine today may produce loose snow avalanches (sluffs) in very steep terrain sheltered from the wind. These slides can be deceptively powerful and can trigger larger avalanches as they move downslope. Pay attention to the terrain above you, and minimize the time you spend below large cliffs and couloirs.  

Avalanche Discussion

The recent storm dropped 2-4" of water (about 2-4 feet of snow) in this zone. Some key observations from yesterday:

  • A group remotely triggered multiple avalanches from safe terrain in the Anderson Ck and Prairie Ck drainages south of Galena Lodge (view Observation and Avalanche reports).
  • In the foothills south of Stanley, Zach remotely triggered a small slide from a ridgeline and experienced widespread snowpack collapsing (watch video, view Observation and Avalanche report).
  • Sun Valley Ski Patrol staff triggered multiple avalanches while performing ski-cutting mitigation work in terrain closed to the public. 
  • Despite the poor visibility, SAC forecasters and other observers saw several natural avalanches in middle and lower elevation terrain along HWY75 near Galena Summit and in the northern Sawtooths near Williams Peak.
  • SAC forecasters, local professionals, and public observers experienced extensive snowpack collapsing—including some that rumbled out hundreds of feet—and some snowpack cracking near Galena Summit and in the Soldier Mtns.

That's a lot of bullseye data. While the storm has ended, the weak layers that were buried in early to mid-December will take some time to adjust to the new load. The deeper snowpack in this zone may make it harder to collapse slopes and/or trigger avalanches, but limited recent observations have us leery of stepping into avalanche terrain or quickly dropping the avalanche danger rating.

Don't trust wind-loaded starting zones or the runouts of large, wind-loaded avalanche paths (due to the chance of remotely triggering avalanches from below). If you choose to play on or under steep slopes, avoiding terrain traps and large avalanche paths will reduce the risk of bad outcomes.

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