Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Small and large wet avalanches are likely to release naturally today. Avoid areas with wet, soggy snow. Do not linger below large avalanche paths. Triggering a slab avalanche large enough to bury a person where the snow is dry remains a possibility on shady middle and upper elevation slopes, especially those with recent wind-drifting. 

Problemi valanghivi

  • Wet Slabs

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

    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:Persistent slab avalanches are possible on NW-N-NE aspects at middle and upper elevations. The natural avalanche Scott observed Tuesday on Bear Peak (photo to right/above) is a great example. The snow that fell in the past 2 weeks buried a snowpack consisting mostly of very weak, sugary faceted snow. These slides can be triggered remotely—from a distance above, below, or to the side of a steeper slope—or by smaller loose snow avalanches coming from above.

  • Loose Wet

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

    Today's intense sunshine and warm temperatures will melt the surface snow, making wet loose avalanches likely. I observed several small wet avalanches yesterday on shady middle elevation slopes in the Lake Creek drainage. These slides will 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 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. Slopes sheltered from the wind are especially dangerous.
    2. On lower and middle elevation slopes that still have a foot or more of snow, regardless of the direction they face.

    Keep a close 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

Snowpacks do not like rapid change. The hot, sunny weather this week is something this snowpack has never seen, and it's predictably misbehaving. 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 updated "Daily Avalanche Form" to handicap the avalanche field:

  • 1:9  Surficial wet loose avalanches: The hands-down favorite again today. I saw at least 60 of these yesterday in the Smoky and Boulder Mtns, and Ben, Chris and other observers counted dozens of additional wet loose avalanches. 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.  
  • 1:1 Natural cornice fall: A new entry in today's race. Cornices will sag under the hot April sun. Some of them will break. They could trigger wet loose or persistent slab avalanches when they strike the slopes below them. 
  • 3:1 Persistent slab avalanches: We saw several fresh, large slab avalanches yesterday, including a monster on Boulder Peak. People triggered at least 4 large avalanches since the earthquake and the storm ended. These are big enough to bury you and can be triggered remotely or fail naturally.
  • 3:1 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. 
  • 3:1 Wet slab avalanches: These will have a better chance of finishing first each day week as the temperatures heat up. 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 this week, 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 and /or cornice fall could trigger slab avalanches lower on slopes as they move downhill. 

Regioni coperte