Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Intense, heavy snowfall and strong wind are creating dangerous avalanche conditions. Avalanches are most likely on steep slopes with wind drifts or stiff snow on the surface but are also possible in terrain more sheltered from the wind. Although unlikely, some avalanches could fail on layers deep in the snowpack releasing a very large and unsurvivable avalanche.

Problemas de aludes

  • Wind Slabs

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

    Today will be the last hurrah in a potent series of storms that began Monday night. Another 5-9" of dense snow is expected today, bringing storm totals to a whopping 2.5-3.5' of snow (2.4-3.2" SWE) by the end of the day. Strong wind blew throughout each storm, blowing from the S on Monday before switching to the SW-W-WNW. Today's wind will blow moderate to strong from the SW, switching to the W by the afternoon.

    Expect to find wind slabs, large drifts, and cornices in upper elevation and exposed middle elevation terrain. Triggering a wind slab is most likely near ridgelines, beneath cornices, and on the sides of cross-loaded gullies. Strong wind has mixed down into valley locations as well, so don't be surprised to find stiffer, wind-drifted snow near the mouths of main drainages and near prominent terrain features lower on slopes. 

    Cracks shooting out in front of you are a clear sign you could trigger wind slab avalanches. Pay attention to how the snow feels beneath your boards or sled. If you feel the snow stiffen or notice you're staying closer to the surface instead of sinking deep into the snowpack, you've found wind-affected snow and should avoid steep slopes. 

    Additional Discussion:Yesterday, high temperatures near Banner Summit reached near freezing. Similar temperatures are expected during periods of the heaviest snowfall again today. This warming has caused rapid settlement in recent storm snow enhancing your chance of triggering a slab avalanche on even wind-sheltered slopes at low elevations. These avalanches should be small but can have big consequences if they drag you into a terrain trap like a road cut or a creek bottom. 

  • Deep Persistent Slabs

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

    A mix of facets and crusts leftover from October snowfall make up the base of the snowpack on most shady middle and upper elevation slopes. Some sunnier, upper elevation aspects have this layer too. To the south of this zone, avalanches have failed on this layer following each major precipitation event.  Because this snow is now deeply buried, it has become much harder to impact it with our weight (see video to right).

    You are most likely to encounter this problem in alpine terrain where the snowpack is variable and thinner places in the slab give you "better access" to the weak layer. This same terrain is also getting loaded the most rapidly by ongoing snowfall and wind. While triggering one of these monsters is unlikely, it's nearly impossible to predict exactly which individual slopes are possible to trigger.

    How are local professionals managing this problem? They are generally taking it off the table by avoiding rocky, alpine terrain with variable snow depths, especially "prime-time" slope angles over about 35 degrees. This travel strategy is pretty easy to swallow given the excellent riding and skiing conditions on slopes lacking the old October faceted snow.

Avalanche Discussion

Snowfall will ramp up again today, hammering Banner Summit, the Sawtooths, and the Western Smokys. Storm totals since Monday evening will surpass 3-4' in these areas by the end of the day. As a result, the danger in the Sawtooth & Western Smoky Mountains Zone remains HIGH. Large, natural avalanches are very likely and avalanche terrain should be avoided. Check out the video Chris and Scott made yesterday while trenching through the storm snow near Smiley Creek. Dangerous avalanche conditions also exist near Dollarhide Summit and Galena Pass where storm totals should reach 3' by nightfall. A sharp gradient in snowfall occurs as you move to the east and south of the Smokys. Far less snow fell in our southern and eastern mountains but dangerous avalanche conditions exist in winder terrain. 

Unlike the disparate snowfall amounts across the zones, it's been windy everywhere. Small, natural, and skier-triggered avalanches were reported above the Wood River Valley in the last two days–occurring on obviously wind-loaded or cross-loaded slopes at middle and lower elevations. This picture Scott took yesterday illustrates the large "dunes" and small cornices that can build lower on slopes. The "lee" or downwind side of these types of features are prime locations to find a sensitive wind slab. The wind has stiffened the snow surface on many slopes in the past few days. Even subtle wind-loading can increase the odds of triggering a soft slab avalanche on steep slopes. Pay close attention to how the snow feels under your feet. If you feel the snow stiffen or notice you're staying closer to the surface instead of sinking deep into the snowpack, you've found wind-affected snow. 

Today's high temperatures will reach into the upper 30s F again today near Fairfield, Hailey, and Stanley. Near or slightly above freezing temperatures will also creep into middle elevations. Warming has condensed the storm snow, creating top-heavy slabs on some lower and middle elevation slopes. These slabs may peel off naturally or be sensitive to your weight. This effect may be amplified in areas like the foothills of the White Clouds, Boulders, Pioneers, and around the Wood River Valley that harbor weaker, shallower snowpacks at lower elevations. I saw small, elk-triggered wet loose slides near Hailey yesterday and similar slides were reported from the Soldier foothills. Across the board, it's good to realize that conditions may change quickly as the day warms. 

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