Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You could trigger wide avalanches up to 2 feet thick at middle and upper elevations. These slides can be triggered from gentler terrain below or to the sides of steep slopes. While it would take some bad luck, triggering a huge, unsurvivable avalanche over 3 feet thick is not out of the question. At upper elevations, you could also trigger smaller slides involving fresh wind drifts.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–3

    Throughout the forecast area, several 1-2 foot thick avalanches (photo 1, photo 2, photo 3) released naturally or were remotely triggered since Friday. These avalanches appeared to involve thin, sun or rain crust + facet layers on slopes commonly exposed to the wind near 9000' (upper or middle elevations). Limited observations indicate that the chances of triggering these slides is lower on SW and S aspects that have thick, hard ice crusts within 2 feet of the surface. 

    This problem is tricky:

    • You can remotely trigger avalanches from gentler terrain below, above, or next to steep slopes (see photo to right/below).
    • You may not experience signs of instability before triggering a large avalanche.
    • Snowpack stability tests are generally providing stable scores on this layer. 
    • The snowpack structure, and especially the crust thickness, can change quickly due to elevation, aspect, wind-exposure, and previous rain events. 

    Many slopes are safe to ski and ride; the challenge lies in accurately determining whether or not a specific slope is safe. All steep slopes in wind-exposed terrain that also have thin crusts located 1-2 feet below the surface are suspect. You can reduce your risk by avoiding these areas as well as slopes with terrain traps or severe consequences (trees, cliffs, etc) in the event you trigger a big avalanche. 

    ADDITIONAL DISCUSSION: While unlikely, we can't rule out the chance of triggering an unsurvivable 3-5 foot thick avalanche involving faceted snow that formed in December. You're most likely to trigger one of these beasts in steep, rocky, wind-swept alpine terrain. Here, thin areas of the snowpack make it easier to trigger avalanches. You are unlikely to observe signs of instability before triggering a huge slide, and accurately assessing stability on a slope scale is next to impossible. Watch this video for more details. 

      

    (2/18/2024) On Sunday, Feb 18th, a skier remotely triggered this large avalanche in wind-loaded terrain from a safe ridge in the Alturas Lake Ck drainage. The slide is an estimated 2 feet thick and likely involved facets that were buried on Feb 1st. N aspect near 8900'. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    You could trigger 1-2 foot thick wind slabs in exposed terrain. Yesterday's wind formed drifts and slabs, and some were sensitive to ski triggering. The fresh slabs may lie above previous generations of wind slabs on some slopes, creating a bigger issue than you might expect. Also, some of the slabs will overlie the persistent weak layer described in Problem 1 or other thin, subtle weak layers that formed in the past week; this can produce avalanches that are surprisingly wide and easy to trigger.    

    Drifts, dunes, rippled snow surfaces, and chalky snow pillows are visible clues that the wind has been at work. If you see cracks shooting out in front of your skis or boards, you've probably found a wind slab. If you feel the snow stiffen beneath your sled or skis, its time to pay attention. 

    (2/20/2024) On Tuesday, Ben intentionally triggered this thin but wide slab on an off-duty ski day in the Sawtooth Mtns. It failed in recently wind loaded terrain, likely on a subtle weak layer that formed during periods between storms this week. In larger terrain, a slab of this size that fails can produce an avalanche easily large enough to bury you.  

Avalanche Discussion

Loose snow avalanches: If skies are sunnier than weather models predict, we may see some surficial sun-induced loose snow avalanches. Whether we call them dry loose or wet loose avalanches doesn't matter. What does matter?

  • These slides release naturally, on their own. Pay attention to what's above you while you travel and when you take breaks.
  • Most of these avalanches should be relatively small, but some could be large enough to knock you over and carry you where you don't want to go. 
  • The threat of avalanches will follow the sun around the compass: E-SE aspects in the morning, S aspects by noon, and SW-W aspects in the afternoon.
  • Very steep, sunny, rocky terrain that is sheltered from the wind produces higher amounts of this type of natural loose snow avalanche activity.  
  • Watch for wet rollerballs moving downslope. These clues tell you the snow surface is becoming damp, and natural avalanche activity could quickly follow. 

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