Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Large human-triggered avalanches failing on layers of weak snow are possible. These are much more likely in wind-affected terrain, but are possible in sheltered terrain as well. Yesterday's storm built thin, relatively small wind drifts and slabs that may be reactive to your weight today. The consequences of being caught in even small slides can be high in terrain with rocks, cliffs, trees, and terrain traps. You can reduce your risk today by steering clear of recently wind loaded slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Several weak layers exist in the upper few feet of the snowpack. A prominent layer of surface hoar buried 1-1.5 feet deep has been responsible for a handful of skier and rider-triggered avalanches in the past few weeks. The most recent slide occurred near Galena Summit on Sunday (report here, photo at right/above). This layer is at its worst on sheltered, shady (W-N-E) slopes. Above this, you'll find a few layers of crusts, facets, and/or surface hoar that were buried in the second half of January. Yesterday's storm added some weight on top of these weak layers and triggering a large avalanche involving them remains possible. In most places you'll need some added load or stiffening from the wind in order to produce avalanches on this layer.

    Older weak layers continue to be worrisome in this zone. Crusts, facets, and/or surface hoar are buried beneath dense, 2-4 foot thick slabs. These hefty slabs make it more difficult to impact these deeper weak layers. You'd be most likely to trigger a slide involving older weak layers in rocky, wind-affected, alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that make it easier to impact these weak layers. There is a lot of terrain that looks like this in the Pioneers, Boulders, and White Clouds. 

    Slides that fail on persistent weak layers are less predictable than simple wind slabs. They may break wider than you expect and may wrap around terrain features that confine wind slabs. Persistent slabs can break well above you on the slope you are skiing or riding on.  Triggered wind slabs can "step-down" to these deeper weak layers, resulting in larger, more destructive avalanches.

    (1/30/2023) This 1-2 foot thick, skier-triggered avalanche failed on a layer of buried surface hoar. Surface hoar is frequently found in shady, partially treed locations like this. N-NE aspect near 9100' in the Salmon River drainage near Galena Summit.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Yesterday's storm brought 2-6" of new snow and a healthy dose of wind to this zone. Wind direction shifted through the storm, building wind slabs on many exposed slopes.  Wind loading and slab growth will continue this morning until wind speeds ease off later in the day. Be on the lookout for fresh slabs near ridgelines and on the sides of mid-slope features like gullies and ribs. 

    Though small, these fresh slabs will be sensitive to your weight today. They are sitting on a variety of weak snow surfaces developed in the time since our last snowfall. As you travel through the mountains, look for signs that the wind has been at work. Dunes, pillows, and ripples on the snow surface indicate that the wind has been transporting snow. If the snow you are moving through is becoming deeper and denser, you're likely moving through wind-deposited snow. Cracks shooting out from your skis or machine are a clear sign of an unstable slab.

    (1/29/2023) This recent small wind slab released naturally on Titus Ridge near Galena Summit. It failed on a E/NE-facing slope at 9,600'.

Avalanche Discussion

In the past month, we've seen the character of the snowpacks in our region diverge. Snowfall in January favored our northern and western mountains, largely missing the Galena Summit and Eastern Mtns Zone. Because of that, the snowpack has remained thinner here and the weak layers we buried in November, December, and January are all still "in play" in this zone.

Several weak layers can be found in the upper few feet of the snowpack. A few layers of surface hoar exist on sheltered, shady slopes, while crusts with and without facets on top can be found on slopes that face the sun. In most places, the slab overlying these weak layers isn't thick enough to produce avalanches in sheltered terrain. You'll be most likely to trigger a slide on these layers in places where the wind has been at work building slabs and stiffening the snow surface.

Weak snow deeper the snowpack continue to be worrisome in this zone. You'd be most likely to trigger a slide involving older weak layers in rocky, wind-affected, alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that make it easier to impact these weak layers. There is a lot of terrain that looks like this in the Pioneer, Boulder, and White Cloud Mountains, which make up the majority of this zone.

At the surface of the snowpack, you'll find yesterday's 2-6" of storm snow. In exposed terrain, the wind has transported this snow into small slabs that are likely to be reactive to your weight today. Look for them near ridgelines and in mid-slope terrain features like gullies and ribs. The wind has been blowing hard enough in this zone that you may find slabs down into middle elevation terrain. Yesterday's storm started warm and ended cold which means you'll find low density snow sitting at the surface. In places where more snow fell, triggering small loose snow avalanches involving the new snow will be possible on slopes steeper than about 35 degrees today. On slopes that face the sun, these small sluffs may occur naturally as the sun warms the snow surface. These slides will start small but will pick up speed and snow quickly as they travel downslope, thanks to the stiff crusts the new snow is sitting on.

Go into the mountains today ready to deal with a range of avalanche problems. Spend a bit of time thinking about the consequences of triggering and being caught in an avalanche in the terrain you are in. Even small slides can have bad outcomes on slopes with cliffs, trees, and terrain traps. 

Regioni coperte