Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Wet snow avalanches are very likely on steep, rocky slopes that face the sun. You could trigger wide avalanches up to 2 feet thick at middle and upper elevations. These slides can be triggered from gentler terrain below or to the sides of steep slopes. While unlikely, triggering a huge, unsurvivable avalanche over 3 feet thick is not out of the question. 

 

Problemi valanghivi

  • Loose Wet

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

    Loose snow avalanches will release naturally on rocky, very steep, sun-warmed slopes. Avalanche activity will follow the sun around the compass: E-SE aspects in the morning, S aspects by noon, and SW-W aspects in the afternoon. These slides start at a point growing in size as they move downhill. Some will be big enough to bury you on large slopes or confined terrain. Watch for herds of wet snowballs or pinwheels moving downslope. These clues tell you the snow surface is becoming damp, and natural avalanche activity could quickly follow.

    Loose snow avalanches can serve as triggers for the Persistent Slab problem described below. Wet slab avalanches may release as meltwater reaches buried weak layers or crusts. Pay attention to what's above you, and don't linger on or beneath steep, sunny slopes. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    Human-triggered avalanches this past week involved weak layers of snow in the upper 2 feet of the snowpack (photo 1, photo 2, photo 3). Most appeared to involve thin, sun or rain crust+facet layers. You're most likely to trigger these avalanches on slopes facing W-NW-N-NE-E-SE in middle and upper elevation terrain, on slopes commonly exposed to the wind. Limited observations indicate that the chance of triggering a slide is lower on SW and S aspects with thick, hard ice crusts within 2 feet of the surface. 

    Persistent Slab avalanches can release in surprising ways. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. Before triggering an avalanche, you may or may not experience snowpack collapsing or other obvious signs of instability.

    ADDITIONAL DISCUSSION: While unlikely, we can't rule out the chance of triggering an unsurvivable 3-5 foot thick avalanche involving faceted snow that formed in December. You're most likely to trigger one of these beasts in steep, rocky, wind-swept alpine terrain. Here, thin areas of the snowpack make it easier to trigger avalanches. Watch this video for more details. 

Avalanche Discussion

Expect to find a wide range of snow conditions and avalanche problems. The near-surface problems are more predictable and easier to identify and avoid, so we'll start there. You can reduce your exposure to loose snow avalanches (Problem 1) by limiting time spent below steep, rocky, sun-warmed slopes. Wind Slab avalanches are possible again today. Recent W and SW wind formed drifts and slabs in exposed terrain. Some of these may remain sensitive to ski triggering, especially where they overlie thin, weak layers of snow in the upper 2' of the snowpack (photo). Steer clear of drifts, dunes, rippled snow, and chalky pillows—clues that the wind has been at work. If you see cracks shooting out in front of your skis or boards, you've probably found a wind slab. If you feel the snow stiffen beneath your sled or skis, it's time to pay attention.

If this is where the story ended, it would be a pretty straightforward day in the hills. Unfortunately, the near-surface problems will play out above the Persistent Slabs described in Problem 2. These hard-to-predict weak layers are challenging to manage. Adding to the uncertainty is how these slabs react to the sun. Loose snow avalanches may trigger a Persistent Slab as they travel down slope. Some slopes may warm enough to push meltwater to these buried weak layers releasing a Wet Slab avalanche. 

Enjoy the beautiful weather, but don't put blinders on. Understand that entering steep avalanche terrain is an uncertain roll of the dice. You can reduce your risk by avoiding slopes with terrain traps or severe consequences (trees, cliffs, etc) in the event you trigger a big avalanche. 

Regioni coperte