Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

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

Kernpunkte

You can trigger 2-3 foot thick slab avalanches that fail on widespread layers of weak snow. Avalanches can be triggered from long distances away from steeper slopes. Smaller loose snow and wind slab avalanches involving the recent snow are also possible. Small loose snow slides will release naturally during periods of direct sunshine. These smaller natural and triggered slides can step down to the weak layers beneath, creating much larger, more destructive avalanches. 

Lawinenprobleme

  • Persistent Slabs

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

    Large, destructive avalanches failing on layers of weak snow buried 2-3 feet beneath the snow surface continue to be a worrisome possibility here. Avalanches that failed on these layers this season have occurred across a range of aspects and elevations. Dig down and you'll find facets and/or surface hoar on shadier aspects and crust + facet combinations on sunnier slopes. These weak layers are impressively widespread and exist on most slopes.

    Slides that fail on these weak layers will break widely and can be triggered from long distances away from the slope that avalanches. Thanks to the very dense slab of snow on top of these weak layers, you aren't likely to get obvious signs of instability as you move through the mountains.  The first indication of instability may be the large, destructive avalanche you trigger. Travel through the mountains knowing that triggering these slides is on the menu.

    (1/22/2024) The debris of this slide ran into a creek, a lower and mid-elevation terrain trap that is characteristic of the Banner Summit Zone. Terrain features like these multiply the consequences of these slides.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Recent storms brought 6-12 inches of snow to this zone. Be on the lookout for minor issues involving this new snow. You may find relatively small wind slabs in exposed upper elevation terrain and will be able to trigger dry loose sluffs on steeper slopes. Periods of bright sunshine today will melt the surface snow, causing a number of smaller loose snow avalanches to release naturally. Slides involving the new snow will be generally small but may run surprisingly quickly on the crusts and stiff surfaces underneath.

    Importantly, these smaller slides can trigger much larger, much more dangerous avalanches on the persistent weak layer described above.

Avalanche Discussion

If you head out into the mountains today, expect to find a beautiful day and dangerous avalanche conditions. The multi-day storm drew to a close last night and we will see some bright sunshine on our fresh snow this morning. Unfortunately, this fresh snow is just lipstick on our persistent slab pig. Across our Forecast area, a layer of impressively weak snow is buried underneath dense 2-3 foot thick slabs of snow. In the past two days, Brooke and I both triggered large and very large avalanches near the boundary of the Galena Summit and Eastern Mtns and Soldier and Wood River Valley Mtns zones. These slides failed hundreds of feet wide and some were triggered from over a thousand feet away. Yikes.

One thing about our current slab+weak layer combination that is particularly concerning to me is how dense the slab has become. The density of the slab helps to keep our skis and machines floating above the weak layer. As we travel around, we may not be getting direct feedback from the snowpack, particularly in our northern and western mountains where the slab is thicker. In areas where the snowpack has remained thinner (southern and eastern mountains) the slab is a bit thinner and triggering avalanches on it will be slightly easier. Across our region, any avalanche you trigger that involves this weak snow is likely to break hundreds of feet wide (or wider) and will send a majority of the snowpack rocketing downslope. Triggering one of these slides is likely today. Direct sunshine will produce some loose snow avalanches on steep slopes that face the sun. These aren't likely to be large, but they can be effective triggers for avalanches that fail on our persistent weak layer. 

Go into the backcountry expecting to be able to trigger large to very large avalanches. These slides can fail in places that you haven't seen them before and can pull back into lower angle terrain above steeper slopes. Triggering avalanches from long distances away is likely today. Be alert to the possibility of triggering one of these slides that affect other members of your group or other groups in the mountains. Today is dangerous. Don't get distracted and don't get complacent. The goal today, again, is to come home safe.

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