Boletín de aludes

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Sun
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Avalanche conditions are dangerous and triggering slides large enough to bury people remain possible. Weak layers exist in the top 3 feet of the snowpack—especially in the Western Smokys—and human-triggered avalanches have occurred in the past week. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. With warming temperatures today, wet sluffs will become possible—primarily at lower elevations.

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Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Late-March storms buried weak layers of faceted snow that formed earlier in the month. Before this most recent storm, human-triggered avalanches occurred in Owl Creek (in the neighboring Galena Summit & E Mtns zone) and in the Salmon Headwaters. Now, these weak layers are buried beneath a 1.5 to 3 foot thick slab and can produce an avalanche large enough to bury a skier or rider

    This past Wednesday, skiers on a ridgeline remotely-triggered a slide on an ENE-facing, 9300' slope on Avalanche Peak near Galena Summit (video above/right). On the same day, riders near Beaver Creek may have also remotely-triggered a large avalanche. Ben was in the Sawtooths yesterday where his snowpack tests yielded unstable results.

    These unstable layers don't exist everywhere, which makes them more insidious, difficult to manage, and more likely to catch you by surprise. These layers are most common in the Western Smokys on slopes that face E-NE-N-NW, but exist in portions of the Sawtooths as well. On these aspects, it's best to assume these layers exist and choose lower angled terrain not threatened by steeper slopes above. Remember that persistent slab avalanches can be triggered remotely—from flatter terrain above, below, and to the sides of avalanche starting zones. 

    ADDITIONAL DISCUSSIONThere are a few other problems to watch out for today:

    • Increasing wind speeds yesterday afternoon and overnight may have created small, fresh wind drifts. Previously wind-loaded slopes are more likely to break down to the buried weak layers described above. Use extra caution on any slope that shows signs of wind loading—including a pillowed appearance, stiffer or denser snow, or a rippled texture. In the Sawtooths, huge amounts of snow collect in cirques and on aprons below large, steep cliff faces. 
    • Warmer temperatures today could lead to wet snow slides, sluffs, and "dribbles". This will primarily be a lower elevation problem but could creep into the mid and upper elevations if the sun stays out longer than forecast.

Avalanche Discussion

What's old is new again. After dealing with widespread persistent weak layers for the first part of the winter, an extremely dry February left us with a stable snowpack and LOW danger by March. But now persistent slabs are back on the problem list—déjà vu anyone?

Many folks think of weak, faceted snow as an early-season phenomenon, but the clear nights and temperature swings of spring can be perfect for forming facet layers at the surface of the snowpack. Often times, these facet layers are mixed in with crusts formed by the sun and warming. During the first half of March, an alternating pattern of small spring storms and clear, cold weather created several of these weak layers. More consistent snowfall in the second half of March has now buried these persistent weak layers beneath 1.5-3+ feet thick slab.  

These persistent weak layers exist throughout the forecast area, but seem to be most common and reactive in the Galena Summit area, the Smoky Mountains (including the Western Smokys and Salmon Headwaters), and the Soldiers. In these areas, there have been four, possibly five, human-triggered persistent slab avalanches since late-March. A number of natural and earthquake-triggered avalanches in recent days appeared to break down to these layers as well. Snowpack observations from our northern mountains have been sparse, but these weak layers may be less common in the Sawtooths and the Banner Summit area—but I wouldn't rule them out.  In the Wood River Valley, there has been less recent loading on these weak layers.

Spring persistent slab problems make me nervous, especially when they follow an extended period of relative stability like we experienced in late-February into early-March. We all seem to understand that these problems are "normal" during the early winter, and we get in the habit of choosing mellow terrain. But by spring, we expect a more stable snowpack and smaller, more manageable avalanche problems. Quite often that's the case—but not always. In fact, our area has had two avalanche fatalities in April, one major injury in late-March, and a number of late-season close calls.

This isn't a typical spring, not on a global scale and not on the scale of our snowpack. There are a number of reasons to ratchet it back out there—and triggering a dangerous persistent slab avalanche is one of them.

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