Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Lawinengefahr

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

Kernpunkte

Triggering an avalanche large enough to bury a person is likely in areas where wind has stiffened the snow surface or built thick drifts. You may be able to trigger these avalanches remotely—from flat terrain below, above, and to the sides of steep slopes. Don't rule out the possibility of triggering a large avalanche in areas sheltered from the wind. 

Lawinenprobleme

  • Loose Dry

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–1.5

    What is it: With late afternoon sunk, natural sluffs, or loose snow avalanches, will become possible. With plenty of low density snow on many slopes, the sluffs could be surprisingly powerful in large avalanche paths.  

    Where is it: You are most likely to find this problem on rocky, craggy slopes that directly face the sun, especially in alpine terrain.

    How do you recognize it: Dry loose avalanches have few early warning signs and are very terrain driven; this problem exists in extreme terrain where recent snowfall has adhered well to rocks or the old snow surface.

    How do you manage it: Timing will be key to managing this problem. Any slope receiving direct sun is suspect. You can manage the threat of these slides by minimizing the time you spend under or on large, sunny, steep slopes, especially in alpine terrain. 

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    What is it: Soft and stiff slabs (1-4 feet thick) formed since Friday. The slabs formed above a variety of weak layers (facets, surface hoar, crusts, and crust + facet combinations). 

    Where is it: Conditions are most dangerous where wind formed drifts or stiffened the snow surface. Avalanches are less likely but possible on steep slopes that are more sheltered from the wind.  The widespread nature of the weak layers means avalanches may be easy to trigger on many aspects and elevations. Avalanches are less likely in lower elevation terrain where recent snow fell on bare ground or is still soft and powdery. 

    How can you recognize it: Watch for stiff snow; snow pillows, dunes, and ripples; and cracks shooting out from your skis, board or sled. These are signs the wind has been at work transporting snow. Assume the weak layers exist on most slopes. Snowpack collapsing or whumphing is a clear sign of unstable conditions.   

    How can you manage it: 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 in the valley bottom is a real possibility. Keep a close eye on your partner and the terrain that's above you.

    Additional Discussion: While less likely, avalanches may fail on weak snow near the ground. The resulting avalanche would be large enough to destroy a house. This scenario is most likely on shaded NW-N-NE facing slopes above about 8,000'. 

    (12/15/2024) This large, natural avalanche released on Saturday or Sunday in wind-loaded terrain in the Beaver Ck drainage in the western Smoky Mtns. E aspect near 10000'. 

    Photo: Ben VandenBos

Avalanche Discussion

Since Friday, the mountains have received a healthy dose of snow (1-2.5" of water, 10-30" of snow). Weak snow including facets, surface hoar, crusts, and, crust + facet combinations are now buried by a thick slab capable of producing avalanches large enough to bury people. Signs like snowpack cracking or collapsing and recent avalanche activity are warnings that conditions are unstable. 

Some recent bullseye data: 

  • Yesterday, near Shaw Mountain, we found weak snow below recent storm snow that produced widespread cracking and collapsing. See this video where Ethan explains this problem well. 
  • On Tuesday, below Titus Ridge, skiers saw a recent avalanche on a NE aspect. 
  • On Sunday, the Sun Valley Ski Patrol triggered several avalanches during mitigation work, before opening to the public. The slides were 12-18" deep and occurred in obviously wind-loaded terrain. While viewing the alpine terrain in the Boulder and Pioneer Mtns, they observed avalanches in wind-loaded areas and large plumes of wind-transported snow.
  • On Sunday, near Banner Summit, a professional reported many plow triggered slides at lower elevations and was able to remotely trigger several additional avalanches. We observed similar unstable conditions (snowpack collapsing and 1 foot slabs fracturing near creek banks) in the valley bottom of the Spring Creek drainage near Galena Lodge.
  • In the western Smoky Mtns, multiple observers reported a large natural avalanche on a NE aspect near 10,000'

Conditions are most dangerous where wind has formed thick, stiff slabs at the surface. Winds will increase through the day, adding more weight to weak layers and building a thicker slab. When the sun comes out today, recent snow that has blanketed extreme, rocky terrain could release naturally if it hasn't already. To reduce the chances of finding trouble, you can choose terrain without signs of wind loading; slopes with fluffy powder on the surface are less likely to avalanche. Slopes with gullies, cliffs, or thick trees increase the consequences of even a small slide. 

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