Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist. You can trigger avalanches involving dense, 2-3 foot thick slabs on many slopes. Winds are building another set of drifts and slabs from the 4-12" of snow that is falling today. These smaller slabs can be effective triggers for deeper, larger avalanches. Triggered avalanches may break wider than you might expect, and can be triggered from a distance away from the slope that avalanches. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Weak snow from November forms the base of the snowpack in many areas. The slab over this weak snow has been building in December and is now 2-3 feet thick. Avalanches failing on this layer will easily be large enough to bury you. Slabs may break wider than you expect, wrapping around terrain features. Triggering slides remotely — from a distance away from the slope that avalanches  — is a real possibility. 

    This layer is at its worst on upper elevation slopes and middle elevation slopes that face away from the sun (W-NW-N-NE-E). Here, a pile of facets is resting on top of a stiff, icy, crusty surface. This combination produced a number of avalanches during loading events and has not had time to gain significant strength. The slab over the weak layer has grown thick enough that it keeps us above the weak layer in places. However, if you are able to collapse the weak layer, the avalanche you create will not be small.

    Brooke and I were in the mountains above Smiley Creek yesterday. We experienced numerous collapses involving this weak snow and received repeated unstable snowpack test results in all 3 of our snowpits. We did not plan on entering avalanche terrain where this weak layer exists, and we stuck to that plan. A nearby observer reported similar findings. 

    (12/4/2023) This large avalanche was observed at 10,000' on the E/NE face of Eureka Peak above the Alturas Lake Creek drainage.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Westerly winds have been blowing at loading speeds since last night, building sensitive slabs in exposed terrain. Today's storm will bring an additional 4-12" of snow to this zone, giving the wind more ammunition.  These slabs exist now and will continue to grow in size and distribution throughout the day.  Look for these slabs near ridgelines and on the sides of mid-slope features like ribs and gullies. Reactive slabs are most likely in upper elevation terrain, but thanks to the strength of the wind you may find slabs extending down into middle elevations. In the steep, rocky terrain of the Sawtooths, these slabs also form on the aprons below large cliffs and couloirs. Textures like dunes, ripples, and pillows indicate that the wind has been at work. Cracking in these fresh wind drifts is a clear indicator of instability.

    These slabs are adding weight to the persistent slab problem described above. Wind slabs that fail can be effective triggers for larger avalanches involving the weak snow near the base of the snowpack.

    (12/4/2023) Cracking in stiff drifts is a clear sign that the snowpack is unstable. This would have been an avalanche in steeper terrain. Galena Peak, Boulders.

Avalanche Discussion

The main driver of avalanche activity this season is a layer of weak snow near the ground. This layer exists on all upper elevation slopes and most middle elevation slopes that face away from sun (northern half of the compass). Continued reports of large collapses in the snowpack are a clear indication that this weak snow is still a problem. Here's a look at how this setup varies across our region:

WETTER AREAS: the mountains in the northern and western portions of our forecast area (Banner Summit area down through the Western Smokys) have been favored by recent storms. Here, you'll find dense, 2-3 foot thick slabs sitting on top of the very weak snow underneath. While the thickness of this slab makes it slightly more difficult to impact the weak layer underneath, continued reports of large collapses in the snowpack are a clear indication that this weak snow is still a problem.

DRIER AREAS: Recent storms have largely skipped over the mountains in the eastern and southern portions of our area. Here, the slab sitting on top of the early-season weak snow is in the 1-1.5 foot thick range. Initially we needed the stiffening and loading effects of the wind to have avalanche issues, but this slab is becoming thick enough to produce avalanche concerns even in areas sheltered from the effects of the wind. 

A storm impacts the region today, adding complexity to this picture. Winds have been blowing at loading speeds for over 12 hours and will continue to blow as the snow falls today. The dry areas described above may only pick up a few inches, while the wetter areas may see as much as 12" with average totals in the 4-8" range. The wind is redistributing large amounts of snow today, building fresh slabs that will be reactive to your weight. Importantly, these slabs are adding weight to the weak snow at the base of the snowpack, increasing the likelihood of triggering a large, persistent slab avalanche. Smaller triggered wind slabs can be very effective triggers for weak layers deeper in the snowpack.

Before committing to avalanche terrain, take an honest account of your understanding of the early-season snowpack. Travel through the mountains knowing that triggering large avalanches is uncomfortably likely today. Pay attention to the terrain you are traveling through and the terrain above you. Large avalanches can be triggered long distances away from the slope that avalanches, and smaller wind slabs may fail naturally. 

Watch Brooke's Weekend Update to get a sense for what's been happening in our snowpack.

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