Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Wet avalanches could release naturally on steep slopes that directly face the sun and on all steep slopes at lower and middle elevations. Avoid areas with wet, soggy snow. Triggering a slab avalanche large enough to bury a person where the snow is dry would require a dose of bad luck but remains a possibility on shady middle and upper elevation slopes with recent wind-drifting. 

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Wet slab avalanches are a problem to avoid, and they will begin to come into play today. Water from snowmelt will percolate down through the snowpack, wetting layers buried 1-3 feet deep that have been dry all year. The snowpack in this zone is very weak and faceted, particularly on slopes that face the northern half of the compass. The facets will behave unpredictably as they get wet for the first time.  This process can result in wet slab avalanches that wipe out much of the season's snowpack. Wet slab avalanches can be triggered or release naturally. These types of slides are both deceptively powerful and almost impossible to accurately forecast on a slope scale.

    Given the power of wet slabs and the difficulty associate with predicting exactly when and where they could release, we have to avoid steep slopes with soggy snowpacks. If the snow surface begins to resemble mashed potatoes, stick to gentler terrain or move to slopes with cooler, drier snow. 

    ADDITIONAL DISCUSSION: Dry persistent slab avalanches are possible on slopes that are not receiving intense, direct sunlight: middle and upper elevation, NW-N-NE aspects. Snow that fell in the past 2 weeks buried a snowpack consisting mostly of very weak, sugary faceted snow. Be cautious on all shady slopes over about 8000' in elevation, especially those with any signs of recent wind drifting.

    Dealing with dry persistent weak layers is a tricky business. Snowpack test results become more difficult to interpret, and you may not see obvious signs of instability like snowpack collapsing or cracking. The first clear sign of an unstable snowpack could be when you trigger a large avalanche. These slides can be triggered remotely—from a distance above, below, or to the side of a steeper slope.

  • Loose Wet

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

    Today's intense sunshine and warm temperatures will melt the surface snow, making wet loose avalanches likely. These slides can occur naturally, without a human trigger. Where the snowpack is thin (less than about 2 feet thick), some of the wet loose avalanches could gouge down to the ground. Where is this problem most likely?

    1. On steep, upper elevation slopes that received more than a few inches of snow yesterday and directly face the sun: NE-E-SE aspects in the morning, S-SW aspects near noon, and SW-W-NW facing slopes later in the afternoon.
    2. On lower and middle elevation slopes that still have a foot or more of snow, regardless of the direction they face.

    Keep an eye on the condition of the snow surface while you're traveling. When it gets wet or when you see wet snow rolling downhill, it is time to move to gentle terrain or slopes where the snow surface is colder and drier. Wet loose instabilities can develop rapidly; think minutes rather than hours. Minimize the time you spend below all large, steep slopes that directly face the sun. 

Avalanche Discussion

The upper 3 feet of the snowpack is officially a mess in much of the forecast area. Choosing which weak layer or avalanche problem to prioritize varies dramatically over space (both weak layer distribution and recent snowfall amounts change as you move up or down in elevation and to slopes that face different directions) and time (how is the intense, April sun changing the stability equation). It's like picking a winner in a crowded, wide-open Kentucky Derby field. With that in mind, here's today's "Daily Avalanche Form" to handicap the avalanche field:

  • 1:1 (even money) Surficial wet loose avalanches: The hands-down favorite today. These relatively small avalanches are most likely on slopes directly facing the sun that received more than a few inches of snow since Sunday night. The mountains near Ketchum, Fairfield, Galena Summit, and Smiley Creek fit this description. While these avalanches will not be huge, they have the finishing kick to knock you down and carry you places you don't want to go. In the wrong terrain, they could be large enough to bury you.  
  • 3:1 Persistent slab avalanches: People triggered at least 4 large avalanches since the earthquake and the storm ended, and most or all failed on weak faceted snow that was near the surface before last week's storm. They are big enough to bury you and can be triggered remotely. They have been living in the Smoky Mtns and Galena Summit area this week, and possibly in the Soldiers as well. You could also find a stray in the mountains closer to Ketchum.  
  • 4:1 Full-depth wet loose avalanches: In areas with a thin snowpack and in rocky terrain, today's intense April sunshine will make larger, deeper wet loose avalanches a contender. Give this choice serious consideration if you're sinking into a thin, wet snowpack or are traveling in or below steep, rocky terrain. 
  • 7:1 Wet slab avalanches: These will have a better chance of finishing first later this week as the temperatures heat up, but they should not be discounted today. These beasts are most likely in the Soldiers and Wood River Valley Mountains where the snowpack is thin (less than 3 feet thick) and weak (lots of sugary facets beneath the snow from March storms). 
  • 7:1 Wind slab avalanches: Although the southern and western part of the forecast area picked up 5-12" of snow the past 2 days, winds were light. In alpine terrain, you could find isolated, soft wind slabs.

Daily Double options: Watch out where these problems overlap. Wind-drifting and persistent weak layers/slab avalanches form a potent one-two punch. Also, small wet loose slides could trigger slab avalanches lower on slopes as they move downhill. 

Regions covered