Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
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

Conditions are dangerous. You could trigger large avalanches involving weak snow near the ground. These are most likely at upper elevations and on middle elevation slopes that face away from the sun. You could trigger slides from gentler terrain below, above, and to the sides of steep slopes. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    You could trigger 2-3 foot thick avalanches that fail on buried persistent weak layers—sugary facets or crust + facet combinations—near the bottom of the snowpack. Assume these old, weak layers of snow exist on all upper elevation slopes and on middle elevation slopes facing the northern half of the compass (W-NW-N-NE-E aspects). Slopes where the wind formed drifts or stiffened the snow surface are most likely to slide.  

    In the past week, every observation we've received noted some form of snowpack cracking or collapsing (observations). These are clear indicators that the snow you're traveling on is unstable. The only surefire way to avoid this problem is to steer clear of steep slopes where these old facets exist. Sunshine melted the early season snow on many SW-S-SE-facing slopes, but it's easy to unknowingly wrap around to a slightly shadier slope with this weak snow near the ground. You can verify the presence of this layer by digging a quick hole. The weak facets will appear grey and feel loose and crumbly (photo).

Avalanche Discussion

To borrow a quote from Utah Avalanche Center forecaster Drew Hardesty, "Persistent weak layers require equally persistent patience." The avalanche danger is slowly decreasing, but each day is only incrementally safer than the last. Benign weather, without additional snow or wind-loading, will help slopes stabilize, but the process is slow. 

The good news is that our persistent slab problem is fairly well-defined (see description above). We've tracked early season snow coverage, watched it facet, and observed how it reacts to storms. We know it can produce avalanches, and we continue to observe cracking and collapsing in the snowpack, signs that many slopes remain unstable. 

The downside to a relatively well-defined problem is our tendency to assume we know too much. As fair weather continues, it will be easy to get complacent, unintentionally reducing our margins of safety. Persistent slab problems are tricky. As conditions improve, you may notice the frequency and spatial extent of collapses decrease. While a good sign, it represents only one small step in the right direction. Where this problem exists, there is no switch to flip or a single piece of evidence indicating a slope is safe.

Entering avalanche terrain is an odds game. The only way to significantly reduce our chance of triggering an avalanche is by sticking to slopes without weak snow near the ground. Where this layer exists, triggering a large avalanche remains a roll of the dice. Given the outcome, let's practice patience as we build a collective case for approaching more complex terrain.

Regioni coperte