Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Dangerous avalanche conditions exist. New snow today will add more stress to an already unstable snowpack. You are likely to trigger an avalanche on most slopes. Avalanches may be triggered both in areas where the wind has built drifts and in areas sheltered from the wind. Slides can be triggered remotely—from below, above, and to the sides of steeper terrain.

Lawinenprobleme

  • Wind Slabs

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

    New snow and moderate to strong winds will be building a fresh round of wind slabs today. Strong winds also blew throughout the storm last week, easily building thick drifts in upper elevation terrain. While these slabs are hazardous in their own right, they are also adding stress to the weak snow described above. Any wind slab you trigger has a good chance of triggering a slide on one of those layers of weak snow.

    (1/30/2021) Avalanches on E-NE aspects in the Deer Ck drainage. Note the interesting patterns of wind loading

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Last week's storm produced a widespread cycle of large, natural avalanches in this zone. Many slides failed at the interface between the old and new snow (about 2 feet down), while others failed on weak snow buried near the ground (about 3-4 feet down). Conditions were already dangerous, and additional snowfall today will be adding stress to this weak snow. The types of weak snow in our snowpack take a long time to heal, and they are giving us plenty of evidence of that:

    • I was just north of Baldy yesterday where I observed an unstable snowpack that produced collapses and unstable results in snowpack test scores. I also observed avalanches on most steep slopes that I turned my eyes to.
    • On Sunday, Soldier Mountain Ski Patrol triggered large avalanches with explosives during routine control work.
    • Yesterday, observers just north of this zone reported experiencing widespread, rumbling collapses involving this weak snow.
    • This weekend, multiple groups of skiers near Galena Summit experienced large collapses of the snowpack, even in areas that have seen significant traffic this year.
    • Further north, in the Beaver Creek drainage, a rider remotely triggered an avalanche that broke up to 3' deep and was large enough to snap a large, dead tree as it descended.

    If this all sounds complex and dangerous then I am doing a good job of describing what you will encounter today in the backcountry. Persistent weak layers are challenging problems to deal with, particularly when they are irregularly distributed. They fail in ways that surprise even seasoned backcountry travelers. The pattern of these weak layers is complex, but the bottom line is simple: if you choose to enter avalanche terrain today, there is certain to be weak snow underneath your feet and you are likely to trigger an avalanche on that snow. 

    You can read more about weak layers in the Forecast Discussion section below.

    (1/30/2021) Persistent slab avalanche near Triple Peaks in the Lake Ck drainage, 8100' NW. Note how this slide over ran the recent ski tracks (appeared to be from during the storm).

Avalanche Discussion

THE EVOLUTION OF A WEAK LAYER

Weak layers in the snowpack don't just magically appear. Generally, they develop at the snow surface and are then buried by subsequent snowfall. After burial, different types of weak layers behave differently. Some are transient, causing stability problems that last for short periods of time, perhaps just a day or two. Others can stick around for weeks or months, causing avalanches every time they are loaded. Right now, we have two main layers of weak snow in our area and we are about to bury a third:

  1. Weak snow near the base of the snowpack: This snow has been buried for almost 2 months and it still keeps me up at night. Up until last week, this layer was responsible for nearly all of the avalanches this season (400 or so). It produced numerous avalanches during the storm and will continue to do so. It is now buried 3-4' down in this zone and any avalanche that fails on this layer is likely to be unsurvivable.
  2. Weak snow underneath the recent storm snow: The character of this layer varies by aspect (the direction a slope faces). On slopes that face the sun, a crust with some weak facets exists (the culprit weak layer in this large avalanche above Baker Lake). Other slopes are holding weak snow without a crust underneath and still others are harboring feathery crystals of surface hoar here.
  3. Weak snow currently at the snow surface: As avalanche forecasters, part of our job is to look into the future and predict how the weather will impact the snow that already exists on the ground. One way we do this is to look at snow surfaces before storms to see what is about to be buried. Yesterday, near Baldy and Sunday in Baker Creek, I observed layers of feathery surface hoar covering the snow surface.

It will take time to sort out which of the new weak layers in the snowpack are most unstable and how long they might be sticking around for. Some of the new weak layers may heal themselves over the course of days while others may be hanging with us for much longer. It takes time for us (and for you) to determine this. Even with days of fieldwork, there is a lot of uncertainty around these things. As we work to resolve some of this uncertainty we will be traveling cautiously and conservatively in the mountains. Alert to the terrain that we are in and the terrain that we are exposed to from above. I strongly urge you to do the same, it is a complex world out there and the likelihood of avalanches is increasing today.

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