Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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In sintesi

You're most likely to trigger an avalanche in areas with stiff drifts or slabs at the snow surface. These slabs could break down to buried weak layers, causing a large, destructive avalanche. Avalanches could be triggered from low-angle terrain, far from where the slide releases. Wet snow avalanches are possible on very steep slopes that face the sun.

Problemi valanghivi

  • Wind Slabs

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    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    You could trigger wind slabs in exposed terrain. The slabs will be larger and more widespread as you climb in elevation. Some of the wind slabs and wind-stiffened snow overlie crusts and crust + facet combinations; in these areas, avalanches could be easy to trigger and could break wider than expected. Small chunks of cornice that you break off or that fall naturally could trigger wind slabs on the slopes beneath them. 

    Fortunately, managing this problem is straightforward; avoiding wind-loaded slopes will significantly reduce the chances you find trouble. Watch for fresh cornices, dunes, rippled snow surfaces, and areas with stiffer snow surfaces. These are clues that the wind has been at work. Cracks shooting out in front of your skis or boards mean you've probably found a wind slab.

    (3/12/2024) This 18" thick wind slab broke near a ridge line in an area loaded by recent SW and W wind. Stanley Lake Ck, NE @ 8,500'. Although this zone has received far less recent snowfall, the strong wind built fresh drifts near ridge lines.  

  • Persistent Slabs

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    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Triggering a large, destructive avalanche is possible. These slides would fail on persistent weak layers (crusts, crusts and facets, or facets) in the middle or bottom of the snowpack. You're most likely to trigger one of these avalanches in areas with shallower snowpacks commonly exposed to the wind.

    Persistent Slab avalanches can release in surprising ways. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. They can break hundreds or thousands of feet wide after several riders or skiers have safely crossed the slope. Before triggering an avalanche, you may not experience snowpack collapsing or other obvious signs of instability.

    We expect to see wet slab avalanches as meltwater makes its way down to these weak layers. Read more in the Forecast Discussion below.

    (3/6/2024) Very large avalanche on a SE aspect above Window Lake north of Boulder Basin. Photo: Sun Valley Heli Ski

  • Loose Wet

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    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Wet loose avalanches may release on very steep, rocky, wind-sheltered terrain soaking in the sun. Expect these slides to run fast and far on stiff crusts. Pinwheels or herds of rollerballs on a slope indicate the snow surface is softening, and loose snow avalanches may soon follow.

    Most of these slides will be small and relatively harmless; however, large slopes, chutes, and couloirs could produce powerful slides that could easily catch, injure, or bury people. Don't underestimate the power of these slides. Be aware of the terrain above you and where an avalanche could carry you. 

Avalanche Discussion

We're in an extended period of high pressure. Significant cloud cover and any chance for snow have moved far to our north, leaving blue skies, light or calm wind, and warming temperatures that peak Sunday through early next week. Wet avalanche concerns will progress from surficial sluffing to full-depth wet loose and wet slab avalanches. The exact progression and timing of these problems are hard to predict and will vary from drainage to drainage and zone to zone. Here are some problems to anticipate as the days heat up. 

This morning will start below freezing, but the mid-March sun packs a serious punch. On sunny slopes protected from the wind, expect to see loose snow avalanches (sluffs) involving snow that's fallen since this past weekend. More recent snow will make these avalanches more likely and larger in our northern and western mountains. Increasing temperatures will shift these sluffs from a mostly dry character to a wet character as a thicker layer of wet snow develops near the surface.

Unfortunately, even shaded slopes won't escape this heatwave. Valley highs will climb into the mid-40s F today and mid-50s F by the weekend. Dry snow will be increasingly hard to find as wet avalanche concerns wrap around the compass. 

As snow melts at the surface, water begins to penetrate the snowpack, eventually draining to the ground. This process can happen quickly in areas with a more uniform, weak, or shallow snowpack, but it can be slow in deeper, stronger snow or on slopes with thick crusts. Weak layers or crusts in the snowpack can impede the water's downward progress, causing the meltwater to pool and increasing the chance of releasing a wet slab avalanche. 

The onset of wet avalanche issues can be sudden, and determining which slopes will slide and when is nearly impossible. When faced with this uncertainty, the only way to reduce our risk is to increase our safety margins. You can limit exposure to these problems by sticking to cooler, shaded slopes where the upper snowpack remains dry. Start and end your day early to avoid the heat of the day, and don't linger beneath steep, rocky slopes baking in the sun.

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