Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

The chance of avalanches will increase throughout the day, and the danger will rise to HIGH by sunset. Expect natural and human-triggered avalanches in windy areas this afternoon. You could also trigger a large avalanche that fails on weak snow buried 1-2 feet below the snow surface in both sheltered and exposed terrain. These thick, powerful avalanches may be triggered remotely—from below, above, and to the sides of steep slopes.

We expect to issue Avalanche Warnings this evening. If you're planning to be out near sunset, stay off of and out from beneath all steep slopes.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Today's snowfall and wind-drifting will stress weak, faceted snow buried 1-2 feet deep. This weak layer has been the culprit in almost all of the avalanches we've observed this season. The terrible snowpack on many slopes in this zone will be "tested" for the first time all year today, and some slopes will fail miserably. 

    We continue to receive reports of obvious signs of instability near the edge of this zone. Some recent, obvious red flags:

    • Multiple groups experienced large collapses and chose to stick to low angle slopes.
    • Chris and Ethan found unstable snowpack structure and unstable test scores (video at right/above) near Dollarhide Summit and Pole Creek.
    • Ben found an unstable snowpack, experienced cracking and collapsing, and got repeated unstable snowpack test scores this weekend in the Owl Creek drainage.
    • Observers near Galena Summit and Baker Creek continue to report unstable snowpack test scores and a poor snowpack structure.

    Be very careful today. This storm will increase the chance of triggering thick, destructive avalanches. Also, natural or human-triggered wind slab avalanches (see Problem 2 below) or large sluffs could "step down", triggering larger persistent slab avalanches as they move downhill. Given the possibility of remotely-triggering slides, avoid terrain with large, steep slopes above you. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Certain
    Size
    1–2

    Today's weather forecast calls for 8-20" of low-density snowfall. Moderate to strong winds will have no trouble forming wind slabs in exposed terrain. The new slabs should be most widespread near upper elevation ridgelines and prominent terrain features, and they will grow thicker and wider this afternoon.

    The fresh slabs will form on a variety of surfaces: wind-hammered surfaces, crusts, weak faceted snow, crusts and facets, surface hoar,  and "generic" old snow. Expect many drifts and slabs to be very sensitive to triggering, and the chance of both human-triggered and natural activity will increase this afternoon. 

    Watch for cracks shooting out from your skis or sled. If you experience cracking on small, safe test slopes, stay off of and out from beneath consequential or large avalanche paths. As the storm progresses, plan to travel more cautiously by increasing your safety margins and avoiding wind-loaded avalanche terrain entirely.  

Avalanche Discussion

Whether I’m in the avalanche forecasting hot-seat or deciding how and where to go play, I usually ask myself three questions to begin my morning routine:

  1. What were the baseline conditions yesterday, and how much uncertainty existed?
  2. Did the overnight weather conditions do anything to change the stability equation?
  3. How is today’s weather going to affect snow stability, and how much uncertainty exists?

The Bottom Line and Avalanche Problem sections of the Forecast speak to these questions, but here’s a bit more nuance:

  1. Baseline: We have an especially ugly, resilient weak layer (facets buried on Dec 11th). It has produced countless natural avalanches with each decent storm, remote-triggered avalanches for many days after each storm, and continued significant collapsing this week (12 days after the last storm and 45 days after the weak layer was buried). The weak layer is widespread across mountain ranges, elevations, and most aspects. It’s more difficult to trigger where buried at least 2.5-3 feet deep, and it hasn’t been a major concern (yet!) where less than a foot of snow lies above it. I don’t trust this weak layer at all where a reasonable slab exists above it, and I’m quite certain of that. Also, we have some weak snow (small facets, crusts and small facets, and isolated surface hoar) at or near the surface. The near-surface weak layers are spatially variable; they change, appear, and disappear as you move to different aspects and elevations. Not all slopes have weak snow near the current snow surface. The weaker snow near the surface is a distant second on my list of weak layers to worry about, but it’s worth remembering as we come into a prolonged storm event.
  2. Overnight weather: Some areas picked up 1-3” of snow (0.05-0.1” SWE), a small load. If it quit snowing now, we’d be looking at pretty much the same hazard picture as yesterday.
  3. Today’s weather: By Thursday morning, the answer is easy in the Soldier &WRV and Galena & Eastern Mtns zones – stay the heck away from all avalanche terrain! Today is tricky, and uncertainty will grow as snow accumulates:
    • Smaller avalanches: Today’s snowfall will be fairly low density (blower powder), promoting sensitive wind slabs near ridgelines and sluffs (dry loose avalanches) in very steep terrain. On some slopes, these small avalanches will naturally release before the weight of the new snow stresses the old faceted weak layer to the point of failure.
    • Larger avalanches: The smaller, “new snow” avalanches moving down slopes could trigger large, destructive slides on the December facets. Also, the weight of the new snow could push the December facets over the brink on some slopes. While I expect this to become more likely from tonight through Friday as snow piles up and temperatures climb, I would not be surprised to see some “foreshadowing” events today.

So where does all of that leave us?

  • Don’t let powder fever get the best of you, especially in the Wood River Valley and Soldier Mountains where everyone has been “jonesing” for face shots all year. When the skiing and riding is really fun, our judgment can become clouded or disappear. We’re effectively hardwired to think “something this good can’t be dangerous.” Keep your head on a swivel.
  • With poor to no visibility, I would not consider playing in or crossing under any terrain with overhead hazard (large slopes over about 30 degrees above you).
  • Small, new snow avalanches (wind slab and dry loose) will become more and more likely as the storm progresses today, especially on slopes steeper than about 35 degrees.
  • The chance of triggering large, scary avalanches on the Dec facets layer – either remotely or while on a steep slope – was already enough to keep me out of most avalanche terrain before today. Adding a steady load from snowfall+drifting and the potential triggers from small slides running down slopes will increase the odds of seeing large, destructive avalanches.
  • MAKE A PLAN TO REEVALUATE YOUR DECISIONS AT SPECIFIC TIMES. Just because you crossed under a path or rode/skied a slope in the morning does not mean it will be safe in the afternoon.

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