Avalanche forecast

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Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Natural wet loose avalanches are very likely on upper elevation slopes that directly face the sun and on all steep slopes at lower and middle elevations. Avoid areas with wet, soggy snow. Do not linger below large avalanche paths. Triggering a slab avalanche large enough to bury a person would require a dose of bad luck but remains a possibility on middle and upper elevation slopes that did not slide during the earthquake. 

Avalanche problems

  • Loose Wet

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

    Today's intense sunshine and warm temperatures will melt the surface snow, producing wet loose avalanches. These slides can occur naturally, without a human trigger. Natural cornice fall can also trigger them. Where the snowpack is thin (near rocks and less than about 2 feet thick), some wet loose avalanches could gouge into deeper layers or 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, 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. 

    ADDITIONAL DISCUSSION: Weak layers of snow buried 2-3 feet deep have proven to be less reactive in this zone than in neighboring areas. On Friday, Chris went looking for this problem north of the highway. He found it in some of his snowpits but not in others. On an east-facing slope, he found a thin layer of facets on top of a crust, all buried beneath a 3-foot thick slab. The block did not fail during standard loading tests in his snowpack tests, but he was able to get it to break cleanly by applying some extra force.

    Weird avalanches tend to happen during the first major, extended warmup of the season. Dealing with persistent weak layers is tricky. Snowpack test results become more difficult to interpret and obvious signs of instability are absent. The first clear sign of an unstable snowpack may occur when you trigger a large avalanche. These types of slides can be triggered remotely—from a distance above, below, or to the side of a steeper slope—or by smaller loose snow avalanches or cornice fall coming from above.

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. 

Regions covered