Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You're most likely to trigger a large avalanche in windier terrain at middle and upper elevations. Slabs of wind-drifted snow sit above a variety of weak snow and crusts. Any avalanches you trigger could be wider and larger than expected.  Human-triggered wet snow avalanches are possible in very steep terrain receiving prolonged direct sun. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Multiple layers of facets and crusts exist in the upper 1-3' of the snowpack. Wednesday, a skier triggered a small persistent slab avalanche near the head of Smiley Ck in the W. Smoky Mountains. The slide failed on a thin layer of facets that formed above a stout rain crust (debris photo, pit photo). Yesterday, this same layer produced unstable snowpack test scores on a slope near Williams Peak in the northern Sawtooths (see Chris' video above, at right). 

    The complex nature of where these layers exist (or don't) makes it hard to pin down a large-scale pattern on which slopes or layers are most worrisome. Two factors that will increase your chance of triggering a slide are slope angle and recent wind-loading. This list combines these factors to describe areas from our expected highest to lowest risk:

    1. Alpine and/or upper elevation slopes greater than about 35 degrees in steepness. The combination of "prime-time" slope angles and thicker, wider slabs thanks to greater wind exposure make these slopes the most dangerous. 
    2. Near treeline or more wind-sheltered slopes greater than about 35 degrees in steepness. While still in the "prime-time" slope angles you'll find thinner slabs at these elevations due to less recent snow and wind. 
    3. Below treeline slopes and those less than about 35 degrees in steepness. Watching slope angles is your most effective tool to stay out of trouble. If you do trigger a slide, it's not likely to be large enough to injure you at these lower elevations where the slab is thin.

    Think about where even a small avalanche would carry you before committing to skiing or riding a slope. Your risk will increase quickly on slopes with terrain traps. These can be trees, cliffs, or depressions where debris can stack up like creek bottoms or gullies. 

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Numerous small, wet loose avalanches occurred on Thursday and Friday. Hot sun peeled away the majority of the "easy-pickings" and natural avalanches are less likely today. However, human-triggered avalanches remain possible on very steep slopes that face the sun.

    These slides are likely to be small, but they can travel quickly on the slick surfaces beneath them. Larger slopes can produce slides big enough to knock you off of your feet and carry you places you don't want to go. Pay attention to how sticky the new snow is becoming. Your odds of triggering one of these slides increase as the snow surface starts to turn to mush. 

    (3/17/2022) Wet loose activity from the past few days. Sawtooth Mountains.

Avalanche Discussion

SHIFTING MINDSET

When writing the forecast we try to take a complex set of snow and weather conditions and distill it down to clear, concise information that will help you plan a safe day in the mountains. Oftentimes we play the "what information would you tell your friend whose visiting from out of town?" game. As Tuesday's storm rolled in, the answer to that question seemed rather simple. We've got a myriad of weak snow layers in the upper 3' of the snowpack. Tuesday's wind and new snow will form slabs that will be sensitive in their own right but may break wider and/or deeper than expected thanks to the weak layers below. If you can identify and avoid wind-loaded terrain, you'd be off to a good start.

Tuesday's storm came and went, and while it was windy at times and even built some small sensitive slabs (observation), it didn't create an obviously wind-loaded environment to look for and avoid. Instead, it masked the previous wind-loading and created a soft, enticing-looking landscape of apparently equal-opportunity powder. It became incredibly difficult to tell which slopes were loaded. The skier-triggered avalanche in Smiley Ck (observation) on Wednesday brought this point home. While less likely, it showed that slab avalanches can be triggered in more wind-sheltered terrain. The slab on this slope was very soft, stiffening only slightly at the base. Our slab avalanche problem is suddenly more insidious—less obvious. So how should we travel?

It's important to remember that the danger is MODERATE for a reason. As Chris states in his video from yesterday (here), this problem does not exist everywhere. To trigger a slide, you'll need to find a steep slope with the overlap of a touchy weak layer and a slab, a combination that exists in only portions of the terrain. The answer to some, mid-winter persistent slab problems is to simply avoid terrain where it exists. In today's problem discussion, I tried to offer some ways to choose safer slopes, based on what we believe to be the most important ways to reduce your risk: keeping your slope angles below about 35 degrees and sticking to more traditionally wind-sheltered slopes that are near and below treeline. 

It's somewhat uncommon to introduce a persistent slab problem this late in the season. By Spring Break, most people are looking forward to a simpler set of avalanche conditions dictated primarily by small wind slabs and diurnal wet avalanches. Those days will come, but we're not there yet. In the meantime, let's reel in our ambitions while we wait for this problem to run its course. 

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