Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Wind drifts exist in exposed, upper elevation terrain. New snow and wind will help these slabs grow today. Be on the lookout for them near features that slow the wind down like ridges and mid-slope gullies and ribs. In the past week, layers of weak snow buried in the upper two feet of the snowpack have produced slab avalanches breaking 1-2 feet deep. These are most likely where the wind has been building slabs but are possible in sheltered terrain as well.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Thin wind slabs exist in this zone. Additional wind and snowfall today well help these slabs grow in size and will keep the possibility of triggering one of these slabs on the table. On Thursday, a skier in the northern Boulders triggered one of these slabs (photo here) and on Friday, skiers in the southern Sawtooths triggered a similar slab (video at right/above). 

    You're most likely to find a reactive slab in alpine, upper elevation terrain where more snow falls and winds are most intense. Be on the lookout for these slabs near features that slow the wind down and force it to drop the load it is carrying. Use snow surface textures (like ripples and dune-like drifts) to help you identify these areas from a distance. If you are traveling through a wind slab, expect the snow to be a bit thicker and denser than snow that is unaffected by the wind. Cracks shooting out from your skis, board, or machine are a great sign that you've found a sensitive wind slab.

    ADDITIONAL DISCUSSIONAlternating periods of sun and snow built and buried layers of crusts and facets in the upper two feet of the snowpack. These layers have proven to be reactive in a few places, particularly on the northern half of the compass. Skiers in the Galena Summit and Eastern Mtns Zone triggered one of these slides yesterday on a north-facing slope at 8,300'.  Triggering one of these slides is more likely in wind-loaded terrain, but is possible in sheltered terrain as well. Read more about this problem in the Forecast Discussion below. 

Avalanche Discussion

The month of March has been marked by unsettled spring weather. Much of our forecast area received measurable amounts of precipitation on 9 of the past 28 days. 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. Periods of storms followed by periods of partly cloudy skies left behind layers of crusts and facets that are buried in the snowpack. Today, with more fresh snow on the way, we will bury another set of these layers.

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 many areas, the bonds at these interfaces are strong enough to support the slab on top of them, but in some they are not. Skiers in the Smoky Mountains encountered one of these weaker areas yesterday when they triggered an avalanche on a sheltered, north-facing slope. Be on the lookout for this problem, particularly in areas where the wind has built stiffer slabs on top of these weak layers. 

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