Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Triggering a dangerous avalanche is most likely on steep, wind-affected slopes. Large natural and human-triggered avalanches were reported this weekend on slopes with exactly these characteristics. Fresh wind slabs will likely be small but may be able to trigger deeper weak layers in the snowpack. Avalanches are much less likely in areas that are sheltered from both current and past wind. 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
    Possible
    Dimensione
    2–3

    The weak snow buried near the ground continues to be the primary avalanche concern in this zone. This layer has produced both human triggered and natural avalanches in nearby zones in the past few days:

    • Saturday, a rider between Wells and Dollarhide Summits triggered an avalanche on a steep, heavily wind loaded slope (photo at right).
    • Saturday, a skier on Titus Ridge intentionally triggered a large avalanche. The slide initiated as a stiff wind slab that formed during last week's wind event and then "stepped down" to the December weak layer. Photos and more details are available here. I looked at the slide that afternoon—watch the video I made.
    • Yesterday, Sun Valley Heli reported seeing a recent large, natural avalanche that failed near the Baker divide, likely involving this weak snow (photo here).

    The depth of the snowpack is highly variable in this zone. This is important because the more deeply this weak snow is buried the more difficult it is to impact. Conversely, in areas where the snowpack is thinner, the weak layer is much more "accessible" to a skier or rider. Last week's prolonged wind event stripped many slopes (bringing the weak layer closer to the surface) and deposited hard slabs on many others (adding weight to the weak layer). This high degree of variability creates a snowpack who's behavior is difficult to predict. This fact has kept many experienced skiers and riders from entering into consequential avalanche terrain, despite the gradually decreasing danger. 

    So what sort of areas should you be most worried about right now? The three avalanches described above share a number of characteristics: they failed in steep (over 35 degrees), rocky, wind-affected terrain. This is exactly the type of terrain where you are most likely to encounter this problem today. 

    ADDITIONAL DISCUSSION:Soldier Cat Ski guides reported that nearly one foot of new snow has accumulated in the Soldiers since Thursday. Several more inches will fall today, accompanied by moderate to strong SW and then NW winds. The combination of the two is creating fresh wind drifts and slabs along upper elevation ridgelines. These slabs will be sensitive to the weight of a rider or skier today. While they should remain small and isolated, remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

    (2/12/2021) This avalanche was triggered by a rider NE of Wells Summit in the Soldier & Wood River Valley zone. The slide broke around 40' wide and carried the rider about 100 yards. A section of the cornice also released in the slide.

Avalanche Discussion

WEATHER FORECASTING Every morning I generate my own weather forecast before reading what the professional weather forecasters at the National Weather Service have to say. As avalanche forecasters, it is important to be proficient in our understanding of both the snow and the weather. After all, the snowpack is nothing more than a record of the weather written in snow and ice. However, there is a lot of uncertainty involved in both of these fields and our true expertise lies in the world of the snow. 

When weather models are in good agreement and the weather patterns are stable it is possible to have high confidence in one's weather forecast. However, when there is a lot of variability between models and we are dealing with shifting weather patterns it is much more challenging to be confident in a weather forecast. This morning, as I looked through numerous weather models and ran them through my own mental model I found myself dealing with a high level of uncertainty in my weather forecast. Different models were indicating different amounts and timing for snowfall and frontal passages. I turned to the weather professionals, and was greeted to this as the first three words of their Area Forecast Discussion: "Another difficult forecast..."  Well, at least I wasn't alone in my uncertainty!

When you are traveling in the backcountry today, think about the uncertainty involved in today's weather forecast. If you were only expecting to see a few inches of new snow and you are finding closer to a foot, think about how that difference may change the likelihood of encountering avalanche problems. If strong winds are blowing and slabs are rapidly building in front of your eyes remember that that observation is more important than the danger rating that you saw in the morning. The avalanche forecast is meant as a starting point for your backcountry travel but it should be a long way from the endpoint. Use the forecast to guide your understanding of the world that you are stepping out into but be prepared to update that model based on your real-world observations. 

Be sure to catch up on the happenings this past week in Ethan's latest Weekend Update.

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