Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

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

Kernpunkte

The snowpack is fragile, complex, and unstable — treat it with respect and build wide safety margins into your travel plans. Slides can be triggered from long distances away from steeper slopes. In the past week, many large human-triggered and natural avalanches were reported, and triggering a large, destructive avalanche remains uncomfortably likely today. Warm temperatures and periods of sunshine will bring wet snow problems to the table. Smaller natural and human-triggered slides can step down to deeper weak layers in the snowpack, resulting in much larger avalanches. 

Lawinenprobleme

  • Persistent Slabs

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

    Snowfall in January built a hefty, 1.5-2.5 foot thick slab over an impressively fragile weak layer. In wind-loaded terrain, the slab may be twice this thick. This combination of slab + weak layer exists on most slopes and has produced countless avalanches in recent days, including a number of large, remotely triggered slides. Dig down and you'll find a layer of snow that resembles an early-season weak layer here: thick facet stacks on slopes that face away from the sun, crusts with associated facets on sunny slopes, and a good helping of surface hoar sprinkled in. 

    Avalanches that fail on this layer of snow will break widely and can be triggered from long distances away from the slope that slides (remote triggering). Small avalanches involving snow near the surface can step down to this weak snow, producing a much larger avalanche.

    At the base of the snowpack, you'll find another layer of weak snow. While less likely, avalanches that step down to this weak layer will involve the entire snowpack and are likely to be unsurvivable (video).

    (1/25/2024) This natural persistent slab avalanche released in the Swamp Ck drainage near 8800' on E and NE aspects (unknown exact release date).

  • Wind Slabs

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

    Expect to encounter a range of smaller avalanche issues in the upper snowpack. Warm temperatures and rain will bring a range of wet snow issues to lower elevations and to slopes that directly face the sun. If the snow you are moving through is moist and you can easily make a snowfall, be alert to these types of slides. As you climb higher into colder, windier terrain, look for small fresh cornices and wind slabs. Steep slopes that haven't been affected by the sun can produce dry loose avalanches. All of these problems are likely to be small, but can be effective triggers for much larger avalanches failing on the weak snow buried in the snowpack. 

Avalanche Discussion

In recent days, the Forecast has been roughly divided into near-surface and older snow categories. The old snow box (Persistent Slab) isn't going anywhere and continues to be our primary concern. However, warm temperatures and rain are changing the nature of the problems that you'll encounter in the upper snowpack. As the snow at the surface melts, small wet snow avalanches will make an appearance. Initially, these aren't likely to be large enough to bury you, but they can knock you off your feet and push you into places you don't want to go. Small loose snow and wind slab avalanches can step down to the persistent weak layer in the snowpack, producing much larger and more destructive avalanches. These same conditions are also changing the properties of the slab that is sitting on our problematic weak layer. This is a much more difficult process to forecast and the result of this surface warming are uncertain. However, we do know that the snowpack doesn't appreciate rapid change and is about to be subjected to a major meltdown that will play out over the coming days. 

Where are you going to get in trouble today? The Banner Summit Zone has a lot of smaller, less obvious avalanche terrain at lower and middle elevations. Here, you'll find many short avalanche paths that end in terrain traps. Imagine sharp road cuts, narrow gullies, and creek bottoms with steep slopes above them. While this terrain can be friendly when stability is good, it is deceptively hazardous on days like today. In recent days, we've seen many avalanches failing in this type of terrain, piling up debris deeply below. As you gain elevation you'll find increasingly thick slabs that have been stiffened by the wind. You can make very large avalanches here, the type that break hundreds to thousands of feet wide. Be suspicious of steep, snow-covered slopes at all elevations.

So how do we manage this problem? Travel through the mountains knowing that you can make large avalanches in many locations. And that the type and location of the slides you make may surprise you. You may find and trigger avalanches in places where you have never seen them before. Or you may see slides breaking much wider than you might expect. Head into the mountains expecting the unexpected today. Start with a conservative plan and stick with it.

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