Bulletin d’avalanche

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
Voir sur la carte

Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions exist thanks to weak layers of snow buried 1.5-3 feet deep. These layers have produced at least 5 human triggered avalanches in the past week. The type of weak snow involved can produce avalanches that fail in surprising ways, breaking wider than you might expect. They can be triggered remotely—from a distance above, below, or to the side. Thin wind slabs that formed in the past two days may be reactive to your weight today, particularly where they rest on weak, sugary snow grains and icy crusts.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Weak layers of snow are buried 1.5-3 feet deep in this zone. Human-triggered avalanches were failing on this weak interface even before the new snow fell earlier this week (photo, photo). In the days since the storm, skiers and riders have triggered multiple slides that failed on this snow. On Thursday, Chris investigated an avalanche near Galena Summit that was remotely triggered by skiers from flatter terrain above. I'd recommend taking the time to watch the video he made, available at right/above. On Friday I went looking for these weak layers in the Sawtooths and I found them. They produced unstable snowpack test scores in my snowpit and I avoided terrain where triggering a slide was more likely than I was comfortable with. 

    The culprit weak layers in all of these slides have been sugary facets that developed in March during clear and cold weather between storms. The distribution and sensitivity of these layers are somewhat irregular. They have proven to be reactive on some slopes and unreactive on others. You are most likely to find them on slopes that face E-NE-N-NW. On these aspects, it's best to assume these layers exist and choose lower angled terrain not threatened by steeper slopes above. These slabs are more likely to be reactive in areas where the wind has stiffened the snow surface and added more weight, but they are possible in sheltered terrain as well.

    Dealing with persistent weak layers is tricky business, particularly as they become more deeply buried. Snowpack test results become more difficult to interpret and obvious signs of instability are absent. The first clear sign of an unstable snowpack may occur when you trigger a large avalanche. 

    ADDITIONAL DISCUSSIONThe days since the recent storm have been much colder than average. Last night's temperatures were the warmest we've seen in a week. If the sun comes out for longer than expected today we may see some wet snow issues develop. Keep an eye on the condition of the snow surface. If it starts to get wet or you are seeing wet balls of snow forming and rolling downhill it is time to think about moving to an area where the snow surface is colder and drier. 

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    A bit of fresh snow and moderate to strong gusty winds have built thin, isolated wind slabs in exposed, upper elevation terrain. These slabs will be most reactive where they are sitting on weak snow surfaces, like sugary facets and crusts. These slabs are unlikely to produce avalanches large enough to bury a person, but they could knock you off your feet or your sled and send you on an unpleasant ride. Be alert to the consequences of triggering such a slide in steeper, rocky terrain. These slabs are also adding stress to the weak layers of snow that are described above. Triggering even a small slide could help to trigger a deeper slide as it travels down the slope.

Avalanche Discussion

Ahhhh, April. A time of good stability, right? Not this year, unfortunately. Skiers and riders have triggered slab avalanches on six out of the past eight days. For perspective, a total of 27 human-triggered avalanches have been reported to us throughout the entire season. Pause and let that sink in for a moment. Nearly one-quarter of the reported human-triggered avalanches occurred last week. 

These avalanches have occurred across much of our advisory area but the layers responsible have proven to be variably reactive. In some places we are seeing clear signs of instability (unstable snowpack test scores and both natural and human-triggered avalanches) while in others they appear to be somewhat inert. This irregular pattern of activity makes these layers even more challenging to deal with. But, with weak layers buried 1-3 feet deep, the consequences of being wrong in your stability assessment can be quite high.

Today, I'd strongly advise that you let the snowpack guide your terrain selection and not the calendar. We are dealing with a snowpack that is behaving more like it is February than April. Its easy to be lulled into the false sense of security at this time of year, particularly after the long periods of relatively good stability that we saw during February and March. But the snowpack doesn't care what the date is and you shouldn't either. In order to avoid the hazards posed by the type of avalanche problems that we are dealing with we need to travel accordingly. Be alert to the terrain you are in and the terrain you are below. Think about the consequences of triggering and being caught in a large avalanche. Your safety and that of your riding partners demands that you ignore the calendar and focus on the snowpack.

Régions couvertes