Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
Open full map
Veraltet — dieser Lagebericht ist 7 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Dangerous avalanche conditions exist. Human-triggered avalanches are likely–especially in recently wind-loaded terrain. Recognize you could trigger avalanches remotely from gentle or flat terrain above, to the side, or from below steeper slopes.

Lawinenprobleme

  • Persistent Slabs

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

    The Banner Summit Zone picked up around a foot of new snow (0.7-0.9” SWE) during the New Year’s Day storm. The weight of this new snow is adding stress to a variety of weak layers in the snowpack. This stress is amplified in areas where dense, thick, wind slabs formed during recent strong wind. 

    Our most concerning persistent weak layers sit near the middle and base of the snowpack. An avalanche failing on one of these layers has the potential to break hundreds of feet wide, spanning multiple terrain features. 

    Slides may be triggered from a distance and have the potential to pull back into low-angle terrain near the top of a slope. Deal with these unknowns by building wide safety margins into your travel plans.

  • Wind Slabs

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

    Recent strong to extreme W, NW, and N wind has raked the forecast area, building wind slabs in exposed terrain (see photo). These slabs will be thicker and more abundant as you climb in elevation. Recent wind-loading may also be found in windier locations at low elevations, such as the mouths of main drainages.

    Extreme wind can cause unusual loading patterns. Expect not only to find wind slabs along exposed ridges and in cross-loaded gullies but also lower on slopes. Cracks shooting from your boards or sled are an obvious sign that you’ve found a sensitive slab. Smaller wind slab avalanches have the potential to step down to more deeply buried weak layers (discussed above) resulting in a very large and destructive avalanche. 

Avalanche Discussion

Observations from the last two days show natural avalanches from Banner Summit, the Sawtooths, the White Clouds, near Galena Summit, the Boulders, Baker Creek, and in the Soldiers. The bulk of the reported avalanche activity failed at the interface beneath our recent storm snow but some failed on one of our more deeply buried weak layers.

Today, triggering a slab avalanche is most likely in recently wind-loaded terrain. Strong to extreme wind formed stout slabs in exposed terrain. These slabs are thicker and more abundant at upper elevations but may be found lower on slopes, especially along main drainages and in the foothills of the Soldiers and Wood River Valley. 

Time will tell whether the interface under the recent storm will continue to be touchy, or if it’ll heal relatively quickly (my vote is for the latter). Yesterday, several observers reported a marked improvement in the bond at this interface. 

Weak layers in our deeper snowpacks have been well documented, and are fairly easy to distinguish. Yesterday, Chris made this nice video describing the snow conditions in the headwaters of the Salmon River. 

In our shallower areas, most notably the central Sawtooths, Boulders, Pioneers, and foothills of the Soldier and Wood River Valley Mountains weak layers are harder to date and differentiate. In many of these shallower areas recent wind slabs and storm snow sit on a thin layer of facets or facet + crust mix on more southerly facing slopes. Two human-triggered avalanches occurred in Croy Canyon in as many days, breaking on these crust + facet layers near the ground. 

We’ve focused a lot on the weak layers in Chris’ video but we can’t lose sight of the fact that these same layers can take on a different look as you move south or turn the corner to more south-facing terrain.

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