Lawinenlagebericht

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Sawtooth Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Triggering a 1-2 foot thick avalanche is likely. Slopes with wind-drifted snow are the most dangerous. While unlikely, avalanches may also break on more deeply buried weak snow producing a very large and destructive slide. Avalanches can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Choose wind-sheltered, lower-angled terrain to reduce your risk.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–3

    We have two persistent slab problems to consider:

    1. Growing Slabs Near the Surface: You could trigger a 1-2' thick slab avalanche on middle and upper elevation slopes. Snowfall over the past several days built a thin, soft slab atop weak layers of small facets or crust + facet combinations. Today's snowfall and wind will continue to grow the slab. The odds that you encounter an unstable slope increase substantially where this slab has been thickened and stiffened by the wind. Look for obvious signs of instability, like snowpack cracking or collapsing. These slides can be triggered from flat terrain—above, below, and to the sides of steep slopes. 
    2. Thicker, Older Slabs: While unlikely, the possibility of triggering a massive 2-5' thick avalanche remains on the table. These very dense slabs also rest on weak facets and crust + facet combinations. This weak layer has been "quiet," meaning we haven't seen any recent avalanche activity or associated obvious signs of instability, but the overall poor structure (slab over weak snow) is hard to ignore. Loading during the next several days of heavy snowfall may be enough to bring this problem back to life. Smaller avalanches may generate enough force to step-down to this weak layer, producing an unsurvivable avalanche. 

    The combination of widespread weak snow, a developing persistent slab problem in the upper 2' of the snowpack, and the uncertainty associated with deeper weak layers should all combine to encourage conservative terrain selection. You can reduce your risk by sticking to wind-sheltered, lower angle terrain. 

    ADDITIONAL DISCUSSION: Expect to encounter thin, sensitive drifts in windier upper-elevation terrain. Look for them near ridgelines and on the sides of mid-slope terrain features like gullies and ribs. Surface textures like dunes, ripples, or pillows are clues that the wind has been at work. Cracks shooting out from your skis or machine are clear indicators that you've found an unstable slab.

Avalanche Discussion

The best way to reduce your risk is to avoid slopes where wind and new snow are forming sensitive drifts. Today's snowfall will be accompanied by moderate wind from the W and NW. These wind directions will begin to form thicker slabs on sunnier slopes with a concerning mix of crusts and facets. Natural wind slab avalanches are possible as wind and new snow rapidly load slopes this afternoon. Smaller natural or triggered avalanches may generate enough force to step down to more deeply buried weak layers. The resulting slide could be massive and unsurvivable. 

Adding to the complexity out there is the chance for a wet, mushy snowpack this afternoon. On many low elevation slopes yesterday, the snow was melting as fast as it fell. Although the snow surface refroze overnight, I'd expect to find wet snow underneath. Today will be another warm day that may weaken the crusts at the surface and push additional meltwater into the snowpack. When this happens, wet avalanches are possible, including wet slabs and wet loose avalanches that gouge near the ground. 

Many of us are used to a more uniform, stable snowpack this time of year, one that's seen multiple waves of meltwater followed by a freeze. So far, the abnormally cool and snowy spring has held off this transition, and our snowpack is in mid-winter form. Use the same caution today as you did during any other large storm this season. Be flexible. Give yourself backup plans and safer exit routes expecting that avalanche conditions will worsen throughout the day. 

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