Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Human-triggered avalanches are possible on steep slopes with slabs of wind-drifted snow. These slides could be 1-2 feet thick and large enough to bury you. Small loose snow avalanches are possible on very steep slopes receiving direct sun. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Expect to find wind slabs at middle and upper elevations. Some of these wind slabs could be over 2 feet thick. Many of them formed above icy melt-freeze crusts, some of which will be sensitive to your weight. At upper elevations on the northern quarter of the compass, slabs overlie a few different weak layers in the upper portion of the snowpack. Any slide that breaks on these weak layers will be larger and more destructive than a simple wind slab.

    Yesterday, Scott came across the debris of a small, but wide slab avalanche near Cape Horn Summit (photo). The avalanche released naturally during the storm on a wind-loaded, middle elevation slope. This was not an "average" storm. Up to a foot of snow fell in this area on Monday. Very strong wind redistributed the snow into drifts and slabs on many slopes (photo at right, below). Expect to find these slabs in both obvious locations (such as near ridgelines) as well as in atypical locations like the side of mid-slope gullies and lower on slopes.

    You can greatly reduce your odds of triggering a slab avalanche by sticking to terrain that is sheltered from the wind. If the snow you're traveling through becomes deeper and denser you've found a fresh slab. Cracks shooting out from in front of your skis or machine are clear indications that the slab you found is unstable. 

    Recent strong winds cross-loaded the sides of gullies, scoured some areas, and created surface dunes and ripples in most exposed middle elevation terrain near Banner Summit.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Loose snow avalanches are possible during the heat of the day. They often originate near warm cliff bands and rocks on very steep slopes that directly face the sun. They begin at a point and fan out to collect debris as they move downslope. They are commonly small but can really pack a punch in large or confined terrain.

    Watch for obvious signs that the warm sun is wetting the surface of the snow. Thinly covered rocks and cliffs will be the first areas to shed. Small roller balls or pinwheels of moist snow can be an early warning that loose snow slides may follow. Pay attention to what's above you. You can largely avoid this problem by sticking to colder, shaded aspects or lower angle terrain.

Avalanche Discussion

Monday was a storm day. Tuesday, aside from moments of warm sun, felt like an average frigid day in early February. Today will be mild and warm in the sun, and high temperatures will climb 15 degrees through Friday. Such is Spring weather in the mountains.

Monday's storm brought 3-6" of snow to the Soldiers and Galena Summit. Up to 12" or more fell in the western Smokys, Sawtooths, and near Banner Summit. The mountains around the Wood River Valley tallied 1-4". Strong to extreme wind raked the mountains. 

Yesterday near Banner Summit, Scott found small slabs, dunes, drifts, and wind-press in most exposed middle elevation terrain (observation). Ben and I found similar conditions in the Smoky Mountains near the headwaters of the Salmon. The slabs we found were sensitive to our weight and were well distributed and large enough to keep us out of quite a bit of terrain (video, observation). To reduce our risk, we chose slopes that were obviously wind-scoured or where the slab was thin.

Many of these slabs fell on a melt-freeze crust that formed during our recent warm spell. Where we've looked, this interface at the base of this slab is fairly friendly. We didn't see any large avalanches yesterday with decent views into the Boulders, Smokys, and Sawtooths. The odds of triggering one of these slabs will continue to decrease, aided by the mild weather—but we're not out of the woods just yet.

I feel that it's easy to underestimate an avalanche problem in the Spring, particularly during or shortly following a spike in danger. Our avalanche brains need to be as responsive as the Spring weather. Triggering a slab avalanche large enough to bury you is a real possibility today; something that hasn't been the case for weeks. 

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