Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanche danger is highest in the eastern portion of this zone—the Little Wood drainage, Pioneer Mtns, and near Bald Mtn—where significantly more snow fell in the past 4 days. There, avalanches are possible even on sheltered slopes. Throughout this zone, watch for wind drifts near ridgelines, especially in upper elevation and alpine terrain. We also expect natural wet loose avalanches with today’s warm, sunny weather. This will be more pronounced on slopes directly facing the sun.

Problemi valanghivi

  • Persistent Slabs

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

    To the east of HWY 75 in the Little Wood drainage, Mormon Hill, and Swede Peak areas of the Pioneer Mtns, over a foot of dense snow fell last weekend, resulting in several large, natural persistent slab avalanches. Some of the slides were hundreds of feet wide (photo to right), failing at the interface between the new snow and the old rotten snow on shadier slopes. With yesterdays’ snowfall and a total of around 18” since last weekend, the Baldy area in the Smoky Mountains also shares this setup. Today, you are most likely to trigger a scary slab avalanche where the wind has affected the snow, but slides large enough to bury people are possible in sheltered terrain too.

    Persistent slab avalanches can break above you, and the 3rd or 4th skier or rider could be the one to find the right/wrong spot to trigger an avalanche. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. Building in some extra safety margin is the only way to safely "manage" this problem. 

    Additional Discussion: In the Soldier Mtns and Smoky Mtns NW of Ketchum, the persistent slab problem is much less likely to exist. However, the light winds and snowfall over the past few days built some soft slabs in alpine and exposed upper elevation terrain. Yesterday I got cracking in fresh drifts at high elevation in the Boulder Mountains, and Scott got reactive test results in the Baker Ck drainage just north of this zone (see photo). The wind slabs appear to be thicker and more reactive on NE and NW aspects where they may have formed above a sandwich of crusts and weak, sugary snow.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    As the sun and warmer temperatures heat up the snow, it will eventually lose cohesion and natural wet loose avalanches will become likely. This problem will be most common where more than approximately 6” of new snow fell in the last few days and the snowpack still exists (no dirt or sage poking through). 

    Fortunately, this problem is fairly easy to manage by keeping close track of the snow surface. 

    • Is the sun directly hitting the slope you’re on or below? 
    • Is the snow getting soft and mushy?
    • Can the snow no longer support your weight if you step off your skis or sled?

    If you find yourself in this situation, it is time to move to cooler, shaded slopes, or the apres-ski.

    Recognize that you don’t need to trigger wet loose avalanches; they have a nasty habit of happening on their own (natural avalanches). Don’t spend more time than you need to below steep, rocky terrain that faces the sun and is sheltered from the wind.

Avalanche Discussion

The avalanche danger scale is a five-step scale that avalanche forecasters use to communicate information about the avalanche hazards you might encounter in the backcountry. Of course, the world doesn't fit neatly into five boxes. There are innumerable shades of gray and subtleties that our simple scale glosses over.  Today, the avalanche danger at upper elevations is mostly MODERATE; however, the type of slide that you might trigger varies significantly over space. Some details:

  • Pioneer Mountains, Little Wood drainage, and Smoky Mtns near Baldy: The southeastern corner of our forecast area got clipped by a significant stream of water since this weekend. While many of our other zones and areas picked up 6-14" of snow, this area is approaching 20" of snow and 2" of SWE (snow water equivalent). This relatively large, rapid load stressed a very weak snowpack for the first time this season; numerous large, natural persistent slab avalanches occurred. These types of slides can be triggered remotely, including from flat ground below avalanche paths—spooky! Dealing with this problem involves building wide safety margins into your travel plans.
  • Sawtooth, Smoky, White Cloud, Soldier, and Boulder Mountains: 6-14 inches of snow fell in the past few days. Light to moderate winds built small slabs in some upper elevation terrain. 
  • All areas with more than 6” of fresh snow on the ground: With the weather forecast calling for a warm and sunny day, we expect to see widespread natural wet loose avalanches involving the surface snow. I don't expect these slides to be large, but they could push you around or carry you into places you don't want to be. 

What tools or travel techniques will you use to manage these problems? The "simple" wind slab and wet loose problems present hazards that are predictable and easily avoidable. If you choose to enter avalanche terrain with this type of problem, you know what to look for and avoid. However, a persistent slab problem is an entirely different beast; you need to "close" large chunks of terrain to effectively manage this problem.

For all of the avalanche types or problems on today's menu, natural and/or human-triggered avalanches are possible—the kicker is the way you deal with the various problems is very different.

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