Bollettino valanghe

Sawtooth & Western Smoky Mtns

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

Large, human-triggered avalanches are likely today—particularly in areas of drifting snow. 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

    Weak layers exist under last weekend's storm snow (about 2 feet down) and near the ground (about 3-4 feet down). I checked in on these weak layers yesterday in the southern Sawtooths, you can watch a short video here.

    Wednesday, 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.

    Today's quick-hitting burst of snow will add stress to these weak layers, particularly in windier locations where fresh drifts formed near the snow surface. 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

    Moderate to strong wind began moving snow in exposed middle and upper elevations yesterday. Continued snow and strong W and NW wind will build a fresh round of wind slabs today. This problem will be more dangerous at upper elevations where slabs will be larger and more widespread. 

    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).

    (2/4/2021) Wind was moving snow yesterday in exposed middle and upper elevation terrain. Snowfall and strong W and NW wind will build fresh slabs in exposed terrain today.

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