Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Tuesday night's snowfall and wind-drifting are keeping the snowpack on edge. Triggering a large avalanche is likely today. You could trigger slides in exposed terrain where the wind has drifted snow and in more sheltered areas with softer snow at the surface. Avalanches can be triggered remotely—from below, above, and to the sides of steeper terrain.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Tuesday night's snowfall and wind-loading were enough to cause natural avalanches and will likely keep many slopes primed for human-triggering.

    Yesterday, Scott observed an array of slab avalanches in the Smoky and Boulder mountains north of Ketchum. Most of these failed in areas with previously wind drifted snow. Some of these slides broke over a thousand feet across, spanning large headwalls in Eagle Creek. We also observed large slab avalanches in Croy Canyon west of Hailey. 

    Meanwhile in the Pioneers, Ben triggered a very large slab avalanche from a safe, low-angle ridge. The slide picked up speed, snapping trees as it careened down a well-defined slide path. The impact of the slide in the valley bottom sympathetically released several other large avalanches. Check out this video here.

    Weak layers exist under this weekend's storm snow (about 2 feet down) and near the ground (about 3-4 feet down). Avalanche activity since Tuesday night is a clear indication that conditions remain dangerous and human-triggered avalanches remain likely. Slides can be triggered remotely—from below, above, and to the sides of steeper terrain.

    (1/31/2021) Debris from an avalanche that was remotely triggered in the Beaver Creek drainage on Sunday. The crown is up to 3 feet thick and the slide was triggered from 100 feet away.

  • Wind Slabs

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

    Up to 10" of new snow fell Tuesday night accompanied by strong wind. Since then, moderate wind blew from the W and NW and is set to increase again this afternoon and evening. Recently formed wind slabs will be thicker and more abundant in exposed, upper elevation terrain. 

    Look for this problem near and below large terrain features and ridgelines. Cracks shooting from your boards or sled are a sure sign that you've found a sensitive drift. Wind slabs may be a problem on their own, but they're also adding stress to buried weak layers. Additionally, any wind slab you trigger has the potential to "step down", causing a much larger persistent slab avalanche (Problem 1 above).

Avalanche Discussion

If you haven't watched the video Ben captured yesterday, 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 weak layers that are the driving force behind our unstable snowpack:

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, and faceted snow, small facets, and some surface hoar (more widespread near Banner Summit). 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 and is not yet showing signs of going to bed. 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 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.

A bit of a wild card is the interface that was buried with Tuesday night's snowfall. Warm temperatures and sunshine formed crusts on many south and west-facing slopes. Surface hoar, observed in the Banner Summit, Galena Summit & Eastern Mtns, and Soldier & Wood River Valley Mtns zones, was also buried.

Tuesday's snowfall and another storm on tap for tonight and tomorrow aren't giving these weak layers a chance to improve. While the intricacies of our snowpack are ever-evolving we have a pile (literal piles) of data that point to dangerous avalanche conditions.

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