Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

A skier-triggered avalanche was reported Wednesday, failing on a weak layer buried about 2' deep. Similar avalanches are likely again today—particularly in areas of drifting snow. While unlikely, we can't rule out the chance of triggering a very large and destructive, 4-foot thick avalanche—especially on very steep, rocky, wind-affected slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    A weak layer of facets and/or surface hoar exists on many slopes, buried under about 2' of snow. Skiers Wednesday on Copper mountain near Banner Summit, likely remotely triggered an avalanche on this layer from nearby lower-angle terrain.

    The slide failed on a thin layer of surface hoar (photo) which appears to be more reactive than locations where only small facets exist. Today's quick-hitting burst of snow will add stress to this weak interface, particularly in windier locations where fresh drifts formed near the snow surface. This layer will remain sensitive to your weight today and triggering an avalanche remains likely in steep terrain.

    (2/3/2021) This avalanche failed 2' deep on buried surface hoar. This weak layer has presented itself as surface hoar in some areas and small facets in others. NE, 8400', Copper Mtn. Photo: Sawtooth Mountain Guides

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    A stout 3-5' thick slab of snow sits atop a layer of facets buried in mid-December. Because the slab over this weak snow is so thick and dense, it is difficult for us to impact the weak snow. However, if you're able to find a spot to collapse the weak layer, the resulting avalanche will be huge and probably unsurvivable. Your odds of triggering a deep slab increase in very steep, rocky, wind-affected terrain where more "trigger points" exist. Trigger points are locations where the overlying slab is thinner and the weight of you and-or your sled can more easily impact the weak layer.  You can reduce the chances of triggering one of these beasts by sticking to slopes less than 35 degrees and avoiding uneven terrain that's peppered with rocks.

Avalanche Discussion

If you haven't watched the video Ben captured Wednesday, you should probably do so now (here). It's amazing how impactful a video like this is. Rather than "just a picture" you can imagine yourself moving with the avalanche, feel its power, and witness its speed. Quite spooky really. Now think again about the size and destructive potential of the other slides observed yesterday like this impressive avalanche in Eagle Creek, this fat slab off Boulder Peak, or this wide avalanche in Croy Canyon near Hailey. These slides paint a humbling picture, one that clearly indicates dangerous avalanche conditions.

There are two main weak layers to keep track of:

Weak snow underneath last week's storm snowThis weak snow formed in mid to late January, and the character of this layer varies by aspect (the direction a slope faces) and elevation. You might find crusts, crusts + faceted snow, small facets, and some surface hoar. Surface hoar was found at this interface yesterday near Galena Summit and Banner Summit, producing poor snowpack test scores. In field reports, you'll see this layer referred to by the date it was buried (1/27).

Weak snow near the base of the snowpackThis snow has been buried for 50 days, but cannot be forgotten. Up until last week, this layer was responsible for nearly all of the avalanches we've observed and recorded this season (approaching 500). This layer of facets has shown signs of improvement in the Banner Summit area and portions of the Sawtooths and now has enough snow above it to begin the healing process in many parts of our forecast area. It won’t happen overnight, or even in a week, but there may be light at the end of the tunnel.

Watch this short video to see what these layers looked like in the southern Sawtooths yesterday. 

Today's angry little storm won't give these weak layers the break they need. While the intricacies of our snowpack are ever-evolving we have a pile (literal piles) of data that point to dangerous avalanche conditions.

Regioni coperte