Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a large, 2-3' thick avalanche is possible. Steer clear of steep slopes with drifts or stiff snow near the surface. Natural loose snow slides (sluffs) are possible on very steep slopes. An approaching storm will increase the danger this evening. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    The weak snow buried near the ground continues to be the primary avalanche concern in this zone. While encountering a wind slab (described below in Problem #2) is more likely, any wind slab you trigger has a chance of "stepping-down" to the weak snow near the ground. Yesterday, I observed this overlap in avalanche problems on Galena Peak. Tuesday in Baker Creek, we saw multiple slab avalanches that were triggered by loose snow sluffs or small cornice fall. 

    Recent avalanche activity shares some characteristics:

    • Slopes steeper than about 35 degrees
    • Wind-loaded terrain
    • Rocky slopes with a thinner snowpack

    This is exactly the type of terrain where you are most likely to encounter this problem today. Recent snowfall has hidden signs of wind events in places, making it more difficult to tell when you're on previously wind-loaded slopes. This fact has made many experienced skiers and riders think twice about entering consequential avalanche terrain, despite the gradually decreasing danger. 

    (2/13/2021) This avalanche was intentionally triggered by a skier stomping on the cornices/wind slab above. It failed on an E/NE facing slope at 9,700' above Titus Lake. The slide initiated in the stiff wind slabs that formed during last week's wind event and then stepped down to the weak snow near the ground as it traveled downslope.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    With 1-2 feet of fresh snow in recent days, it doesn't take a lot of wind to form slabs. Tuesday, we saw sizable natural avalanches in alpine terrain in the Smoky Mtns (video to right/below, Observation), and snowfall and wind continued since then. Expect to find widespread wind slabs in exposed upper elevation terrain and in cirques beneath large cliff bands. Watch for and steer clear of slopes with drifting and with cornices on the ridges. 

    ADDITIONAL DISCUSSION:On very steep slopes, natural and human-triggered loose snow avalanches (sluffs) are possible. This problem is fairly simple to manage—be aware of the terrain above you, especially if it's sunny. Remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

Avalanche Discussion

In the past few weeks, snowpack characteristics have diverged significantly across our forecast area. In our northern zones, we are primarily dealing with "new snow" avalanche problems including fresh wind slabs created by new snow + wind as well as loose snow avalanches in very steep terrain. Less snow has fallen in our southern zones and an overall shallower snowpack has kept persistent weak layers or "old snow" avalanche problems at the top of our problem list. Here's a quick rundown to highlight some of these differences. 

Banner Summit and Sawtooth & Western Smoky Mountains:In many ways, the snowpack in these northern zones is simplifying. The rise and fall of avalanche danger here is primarily tied to storm activity. In the last week, a series of storms have deposited anywhere from 2-3.5' of snow (2-2.5" SWE). The ebb and flow of NW wind built wind slabs in exposed terrain. The Banner Summit area, with overall lower elevations and less steep alpine terrain, tends to keep its head out of the wind a little better than the Sawtooths. For this reason, the avalanche danger has remained elevated in the Sawtooths where both wind slab and loose snow avalanche problems are more prominent. 

Weak layers in these zones do exist. In fact, it's likely that the snowmobile-triggered slide near Cape Horn Summit on Tuesday involved a layer of weak facets and surface hoar that we've been tracking since late January. This avalanche (if indeed attributed to this weak layer) bucks a trend of improving stability in the past week. So, as tempted as we may be to toss this avalanche aside as an outlier, that's not how it works—more information is warranted. The primary weak layer of concern in our southern zones, and the one which produced extensive natural and human-triggered avalanche activity earlier this season is buried under a hard 4'+ slab of snow. Triggering an avalanche on a weak layer this deep is unlikely. 

Galena Summit & Eastern Mountains and Soldier & Wood River Valley Mountains:In our southern zones, the waters are much murkier. Here, we're dealing with a highly variable snowpack both in recent storm totals and overall snow depth. The one constant tying these areas together, and what makes them much different than our northern zones is the overall shallower snow depth. In areas where the snowpack less than about 4' deep, our likelihood of impacting weak facets near the ground increase. 

The rise and fall of avalanche danger in these zones is still very much influenced by the presence of weak facets near the ground. It may take less snow + wind to see a spike in avalanche activity and the threat of human-triggered slides can persist for several days after a storm. In these zones, the possibility for small avalanches or cornice breaks to "step-down" to these facets is very real. 

Régions couvertes