Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Dangerous avalanche conditions exist. Skiers and riders could trigger large, destructive avalanches. Wet avalanches are possible on sunny slopes this afternoon if the snow surface turns to mush. Choose conservative terrain and build in a large safety margin. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

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

    You could trigger a 2-4' thick persistent slab avalanche. Buried weak layers (sugary facets or crust + facet combinations) were overloaded by recent snowfall, wind-blown snow, and rain, producing hundreds of avalanches in recent days (map). Some slopes are simply waiting for a trigger to push them over the edge. 

    Limited observations indicate the weak layers are not as widespread in this zone, but the safe bet is to assume they exist on any given slope until proven otherwise. Slabs will be more sensitive to triggering where recently wind-loaded. You can identify these slopes by the stiffer, denser snow that keeps your skis or sled from sinking deep into the snowpack.

    Unfortunately, you can't out-smart this problem with small-scale route finding. This is the type of problem that may not offer obvious signs of instability, like snowpack cracking or collapsing. Tracks on a slope do not mean it's safe. Avalanches can be triggered by the second, third, or fourth rider. They may break over 1,000' wide and several feet thick. If caught, many of these slides will be unsurvivable. Use caution today. You could remotely trigger avalanches from gentle terrain far above, below, or to the sides of steep slopes.

    Additional Discussion: Triggering a wind slab avalanche is possible in recently wind-loaded terrain. Wind slabs are more likely at upper elevation. Look for smooth pillows of windblown snow near ridgelines and mid-slope terrain features like ribs and gullies. Wind slabs or a failing cornice can serve as an effective trigger for the larger and more dangerous persistent slab problem described above. 

    (3/12/2023) This avalanche failed on a SE slope at 9000' in Lola Creek. Based on the aspect and the appearance of the crown, this slide likely failed on a layer of facets below a melt freeze crust.

Avalanche Discussion

Last weekend, a snowmobiler was tragically killed in an avalanche. The danger was not obvious. As they rode in, their group did not observe any nearby natural avalanches or other signs of instability like snowpack cracking or collapsing. The fatal slide was not triggered by the first or even the second rider on the slope. It was a sunny, beautiful day following a large recent storm. Today is a carbon copy of that day. Please be careful out there.

The conditions you experience at low elevation trailheads this morning are far from what you should expect as you climb in elevation or as temperatures warm into the afternoon. Here are some considerations as you plan your day:

  • As you climb, so does the danger. Expect to encounter a host of avalanche problems at middle and upper elevations. It may finally start to feel "spring-like" around town in the Wood River Valley, but don't be fooled, the mountains still have a layered, mid-winter snowpack. If you're driving to Galena Summit, the danger is real, and it begins right from the road (photo).  If you start the day at low elevation, expect the danger to increase as you climb out of areas with stout crusts and enter terrain with thick, dry slabs and recently wind-blown snow. In addition to the persistent slab and wind slab avalanche problems discussed above, large sagging cornices guard the rims cirques. These massive overhanging chunks of snow are unpredictable and can spontaneously release. They are dangerous in their own right but may also trigger a slab avalanche as they tumble downslope. 
  • Warm days = wet avalanches. A hard freeze last night may have turned some low elevation slopes into an ice rink (photo). This time of year, however, the hot sun can soften surface crusts and pump water into the snow. This process increases the odds of both wet loose avalanches and wet slab avalanches in the afternoon or evening before the snowpack has a chance to firm up again overnight (photo). Keep this in mind if you plan to be out late in the day, especially if your return route brings you through or beneath W, SW, or S-facing terrain. 

Today's avalanche conditions deserve your respect and attention. It's a day when you can feel like you're doing everything right, get comfortable, and inadvertently stray from your plan. Get out in the mountains and enjoy this beautiful day; stability is improving, but don't let your guard down. Keep your objectives conservative as the snowpack adjusts to recent storms. 

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