Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Human-triggered avalanches are likely. The combination of 5-9" of new snow + wind will build reactive slabs and add stress to the layer of very weak snow buried 1-2.5 feet down. Smaller triggered slides may step down to this layer, producing much larger avalanches. Pay attention to the terrain around you and above you—slides may be triggered from long distances away from steeper slopes.  Cracking and collapsing of the snowpack are clear indicators that the snowpack you are traveling in is unstable.

Avalanche problems

  • Persistent Slabs

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

    The recent storm deposited 2-2.5' of snow (1.7-2.0" SWE) on an exceptionally weak layer made up of crusts, facets, or a combination of the two. This combination produced a widespread natural avalanche cycle, with slides observed on all aspects and at all elevations. You'll find this combination of a thick slab overlying a reactive weak layer almost everywhere you go today. The slab of new snow is thick enough that the wind doesn't need to have done any work to build a slab—avalanches are possible in both sheltered and wind-affected terrain.

    Yesterday, riders in the Baker Creek drainage reported triggering small slides on road cuts as they rode by. I was also in Baker Creek yesterday where I experienced collapsing and shooting cracks and chose to travel knowing that remotely triggering avalanches was a very real possibility. A collapse on mellow terrain at the valley floor can quickly travel long distances and release avalanches on steeper slopes far above. Pay close attention to the terrain around you and above you. Remember that there are other people out in the mountains and that impacting them and being impacted by them is possible. Stormy conditions today will make it easy to become disoriented and to lose sight of what is above you.

    Many lower-elevation slopes that face S-SW-W in this Zone were free of snow before last week's storm and this weak layer does not exist there. However, as you travel around the compass to colder aspects you will find this same weak snow.

  • Wind Slabs

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

    Today's storm will bring 5-9" of new snow, moderate to strong, gusty winds, and mild temperatures. Wind slabs will build quickly under these conditions. These slabs will fall on a relatively weak snow surface and I expect fresh slabs to be touchy today. In addition, they are adding stress to the weak layers described in the persistent slab problem above. Natural or triggered wind slabs can make for "great" triggers for bigger avalanches on deeper weak layers as they run downslope.

    An uptick in wind speed yesterday (without new snow) was enough to produce at least two natural avalanches—a large slide in the Boulder Mountains east of Galena Summit and a smaller slide in the Beaver Creek drainage west of Smiley Creek (pictured at right, observation here). Similar slabs will be growing in size and distribution today. 

    (12/3/2022) The small wind slab was observed on December 3 onan E-facing slope at 9,300' in the Beaver Creek drainage. It likely failed thanks to an increase in wind speed reported by remote weather stations on 12/3. Older debris is also visible in this photo.

Avalanche Discussion

Today will be more dangerous than yesterday. I would not be surprised to see some large, natural avalanche activity out of this storm, particularly if snow totals come in at the high end (8-10"). An uptick in wind speed yesterday (without new snow) was enough to produce at least two natural avalanches. New snow and wind will help slabs at the surface to grow larger and more reactive.

Let's spend a minute thinking about what is changing in the snowpack today. Warm and wet air is pushing into the region and has helped mountain temperatures to climb overnight. All of our remote weather stations are currently reporting below-freezing temperatures (32 F), but not by much. Temperatures will hover on either side of freezing as a quick-hitting band of precipitation passes through during the day. These warm temperatures will help the new snow bond to itself, producing quickly building slabs. These slabs are falling on top of a snowpack with a widespread layer of weak snow buried 1-3 feet down. Even though this storm will bring only a fraction of what fell last week, it will be adding structure to the existing slab. 

The properties of a slab are a critical portion of the avalanche equation  [ slab + weak layer + trigger = avalanche ].  Our weak layer hasn't changed significantly since yesterday, but the slab is about to. Recent research has clearly shown that adding even a thin slab on top of unconsolidated snow can make conditions much more favorable for producing avalanches. Today's wind slabs will have a similar effect on our snowpack and will keep the mid-November drought weak layer sensitive to your weight. These new slabs will also make for effective triggers for weak layers in the snowpack. Add in the fact that stormy conditions will make it hard to identify avalanche terrain around you. It's a good day to take a step back as the snowpack complexity increases.  

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