Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
Ver en el mapa

Peligro de aludes

Tue
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
Open full map
Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

New snow and freshly formed wind drifts are stressing the thin and weak snowpack that exists in this zone. Danger will likely increase to CONSIDERABLE overnight. Avalanches will be most likely where the wind has built slabs, but are possible in areas sheltered from the wind. In the eastern portion of this zone (the Little Wood drainage, southern Wood River Valley, Pioneer Mtns, and near Bald Mtn), a slab already exists on this weak snow and avalanches are possible without additional loading. Rain on snow at lower elevations will increase the threat of loose snow avalanches as the day progresses.

COVID-19: Please recreate responsibly close to home. The medical system cannot spare the resources to care for backcountry skiers and snowmobilers. Follow social distance requirements to protect yourself and others. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    A thin, weak snowpack exists in most of this zone. Storms in March dropped 1.5-2 feet of snow in the eastern portion of this zone, which produced a concentrated avalanche cycle. Many slides failed hundreds of feet wide (photo at right/above). Triggering an avalanche involving this weak snow is a possiblity today, even without additional loading. As more snow falls today and the wind builds fresh drifts, the likelihood of triggering a slide on this weak snow will increase. Avalanches will be most likely on recently wind-loaded slopes, but they can occur on slopes that are sheltered from the wind as well. Even in the absence of this weak snow, thin wind slabs that form today may be sensitive in upper elevation terrain.

    Persistent slab avalanches can fail in ways that catch even experienced backcountry users by surprise. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. Choosing lower angled terrain not threatened by steeper terrain above is the only way to safely "manage" this problem. While these avalanches are most likely on recently wind-loaded slopes, they can occur on slopes with no recent wind-drifting as well. 

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1

    Warm air temperatures and rain at lower elevations will increase the hazard of wet loose avalanches today. Slides will start at a point and fan out as they travel downhill. If enough rain falls, these slides may gouge through weak, wet snow to the ground. Many slopes at lower elevations aren't steep enough for this type of problem. Unfortunately, quite a few of the ones that are steep enough sit above terrain traps, like gullies and creek bottoms. In these areas, avalanche debris from even a small slide can pile up deeply enough to bury you. 

     

Avalanche Discussion

The month of March has been marked by unsettled spring weather. Much of our forecast area received measurable amounts of precipitation on 10 of the past 29 days. It looks like today we will make that 11 out of 30. In between these stormy days we've seen patchwork skies with a mixture of sun and clouds depending on your location. Let's take a minute to think about how this affects the snowpack:

Intense spring sunshine can quickly melt fresh snow. After this wet snow refreezes, this process tends to result in a strengthening of the snowpack. Simple enough. However, when the sun starts to melt the snow but clouds put a halt to the process something else happens. A thinner, more fragile crust is left behind in this case, often accompanied by some small, angular snow crystals known as facets. Warm ambient air temperatures can also build these sorts of layers. Periods of storms followed by periods of partly cloudy skies left behind layers of crusts and facets that are buried in the snowpack. Light snowfall yesterday helped to bury another set of these layers and continued snowfall and wind drifting today will add stress to the underlying snow. 

The tricky thing is that these layers have proven to be variably reactive. Why is that? Our forecast area spans quite a large chunk of terrain, over 3000 square miles. On any given day, the weather varies significantly across this area. Passing clouds might provide some cover for one mountain while the sun is shining brightly on a neighboring mountain. But the weather isn't the only important factor in this equation. The direction a slope faces and the steepness of the slope both affect how much incoming solar radiation hits the slope. Because of these factors, the character of the weak layers that are buried in the upper portion of the snowpack varies from slope to slope. In some areas, the bonds at these interfaces are strong enough to support the slab on top of them, but in others they are not. On Saturday, skiers in the Smoky Mountains found an area where this interface was weak when they triggered an avalanche on a sheltered, north-facing slope.

Today will be a transitional day for the snowpack in our region. By tomorrow morning many areas will have been hit with a more substantial load than they have seen in weeks. This new snow will be accompanied by increasingly intense winds, a great combination for building wind slabs and adding weight to the snowpack. This loading event will help resolve just how widespread and reactive the weak layers in our snowpack are. If you decide to head out today, particularly this afternoon, I'd recommend dialing back your terrain choices and treat these layers as guilty until proven innocent. 

Regiones cubiertas