Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Weak layers of snow buried 1-3’ deep continue to keep the avalanche danger elevated. Triggering an avalanche on one of these layers is not likely, but the resulting slide would be large and destructive. In addition, yesterday’s northeasterly winds built thin slabs in exposed terrain that may be sensitive to your weight today.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Weak layers of facets and depth hoar are buried near the base of the snowpack in this zone. As time passes without major loading events, triggering a slide on one of these layers becomes unlikely. But unlikely things do happen.

    Yesterday, in the White Cloud Mountains, I looked at the aftermath of a large avalanche (photo here) that failed on weak snow near the ground on Sunday. This avalanche broke over 500 feet wide, 4-6 feet deep, and wiped out the majority of the season’s snowpack, covering snowmobile tracks from the previous day. It is unclear if this avalanche failed naturally or remotely triggered from below. While the overlying slab is much thinner in this zone (see photo at right), it is underlain by similarly weak snow. 

    This is the sort of problem we are dealing with when we talk about weak snow at the base of the snowpack. Be aware that even if you aren’t directly in steep terrain yourself, the snow that you are traveling on may be connected to that sort of terrain.

    ADDITIONAL DISCUSSIONYesterday, the combination of wind blowing from an unusual direction (northeast) and a few inches of new snow was enough to create natural avalanche activity in the Boulder Mountains (photo). This zone has picked up very little snow recently, but the shift in wind direction may have been enough to pick up some of the older snow that was sitting around in sheltered areas and create thin, isolated wind slabs. You are most likely to encounter one of these slabs near exposed terrain features such as ridgelines and along rocky ribs and gullies in the middle of slopes. These slabs are adding stress to the weak layers of snow near the ground described above.

Avalanche Discussion

You might have felt like our snowpack was tricky to deal with already, but yesterday’s weather showed us that things can always get worse. A touch of snowfall on Sunday, coupled with an intense wind event on Monday have complicated the avalanche picture. We are dealing with two very different hazards right now:

  1. Despite the lack of fresh snow, strong winds blowing from an unusual direction (NE) were enough to put a large amount of snow “into play” yesterday. These winds quickly built slabs, many of them in locations where you might not expect to find wind slabs with more usual wind directions. Natural activity involving these wind slabs was observed in the Boulder Mountains.
  2. Buried deeply in the snowpack are several layers of weak snow. These persistent weak layers create difficult to predict and manage avalanche hazards. An avalanche on depth hoar near the ground in the White Cloud Mountains on Sunday (described above) is a clear indicator that avalanches involving this weak snow are possible.

Dealing with either of these problems individually is challenging in its own right. But currently these beasts are dwelling in the same lair, and they are interacting. The fresh, stiff wind slabs are adding additional weight to the weak layers below. But that's not all; they are also adding structure, providing a medium that can help to “communicate” a fracture across features that otherwise might constrict the dimensions of a slab. Do I think it is likely that we will see natural or human triggered avalanche activity on our buried weak layers today? No. But will I be travelling with the knowledge that these difficult to predict weak layers could potentially fail and cause a large, unsurvivable avalanche. Absolutely.

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