Avalanche forecast

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Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanches are most likely in exposed, upper-elevation terrain where new snow and wind combine to form sensitive drifts. Smaller avalanches on upper elevation, north-facing slopes have the potential to break into weak snow at the base of the snowpack. You could also trigger loose snow avalanches (sluffs) in steep terrain.

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Avalanche problems

  • Wind Slabs

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

    New snow and wind created wind slabs in exposed terrain. You're most likely to encounter this problem at upper elevations where snow totals are greater and wind speeds are higher. This morning's snow fell with a moderate wind from the south. Wind will shift to blow from the west by midday as snowfall diminishes. This means the bulk of today's fresh wind slab will tend to favor more northerly aspects–slopes with some of the weakest underlying snow.

    Any freshly formed slabs are likely to be sensitive to your weight. Yesterday in the Smoky Mountains, I triggered a few small drifts that formed earlier this week. Today's storm will build similar slabs that will be a bit thicker and more widespread. 

    Cornices, ripples, dunes, or wave-like patterns in the snow can help you identify freshly loaded slopes. Cracks shooting from your boards or sled are a sure sign that the slope you’re on is unstable. A shallow wind slab that begins near the snow surface has the potential to break into deeper weak layers of snow near the ground. 

    Additional Discussion:Although slab avalanches are most likely in areas affected by the wind, it's also possible to trigger thin slabs in more sheltered terrain–particularly where new snow amounts reach 8 inches or more. We've got a grab bag of weak snow surfaces beneath today's snowfall. Use small, steep slopes or dig quick hand pits to keep tabs on how well the new snow bonds to what's underneath. As the snowpack is primarily comprised of sugary facets, loose snow avalanches (sluffs) remain possible in steep terrain. 

    (12/16/2020) New snow and wind will help create small stiff drifts and slabs in exposed terrain. This sensitive drift was observed Wednesday in the southern Smoky Mountains.

Avalanche Discussion

I feel honored to put the first splash of color (a yellow star) atop our lonely (so far all green) tree of LOW danger. MODERATE danger at upper elevations is our first bump in danger since beginning daily Backcountry Avalanche Forecasts on Sunday. This increase in danger is in response to the storm that by mid-morning will bring 5-10" of snow and moderate wind. 

For weeks we've been showing you videos of weak, sugary facets both at the ground, near the surface, and in shallow snow areas throughout the entire snowpack. This weak snow, while cool to look at and interesting to ride was generally stable. Aside from sluffing in steep terrain, there's been a very low probability of triggering a large avalanche. So what was the missing ingredient? The answer, a lack of a cohesive slab of snow near the surface–that changes today.

South wind during and shortly after today's storm will focus new slab development on shadier, north-facing terrain. These slopes also harbor some of the weakest snow we've seen this season (or any season for that matter). Expect to find sensitive slabs anywhere the wind has stiffened the recent snowfall. Thin, touchy slabs may also be found in more sheltered areas where snowfall is greater.

Today's heaviest wind-loading overlaps locations where sugary faceted crystals are buried at the base of the snowpack–primarily shady, upper elevation terrain. A wind slab avalanche has the potential to step down into this weak snow near the ground. The resulting avalanche would be large and destructive.  Because of the potential consequences, we've been avoiding avalanche terrain where this layer exists. 

The stability equation prior to today was relatively simple. Adding a slab near the surface changes the picture entirely. I'll be heading out with the goal of reassessment and I'd encourage you to do the same. How is the new snow bonding to the old snow at different elevations and on different aspects? Is it better or worse in areas with crusts near the surface? Where am I finding sensitive drifts? How big are they? These are all helpful thoughts to keep in mind as we see how this generally weak snowpack reacts to its first decent storm. 

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