Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Dangerous avalanche conditions exist. Triggering 1-3 foot thick avalanches is likely today.  Avalanches will be easier to trigger in terrain affected by the wind, but are possible in sheltered terrain as well. Avalanches can be triggered from long distances above, below, and to the sides of steeper slopes. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2

    What is it? A significant amount of natural avalanches occurred in the last 48 hours. Most of the larger avalanches were in areas where the wind has added additional weight to the recent snow. Today, you can trigger the same sensitive 1-3 foot thick slabs in many areas with wind-affected snow.

    Where is it? These slabs will be the largest and thickest at upper elevations, but you'll also find wind slabs in exposed middle-elevation terrain. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like couloirs, gullies, and ribs. The rocky nature of the Sawtooth Mountains allows new snow to run down the sides of cliffs and build up additional weight in the aprons. In these locations, it is also likely to trigger slab avalanches today.

    How can you recognize it? Cracks shooting out from your skis or sled and collapsing clearly indicate instability. Look for ripples in the snow, dunes capping ridgelines, and drifts along the sides of gulleys or chutes. Wind-deposited snow will be stiffer and keep your skis or snowmobile on or closer to the surface. Some of these slabs might be masked by recent snow and be more hidden.     

    How can you manage it? Most wind slabs are building on top of persistent weak layers in the snowpack (read Problem #2 below). Because of this, the wind slabs you encounter today may behave more like persistent slabs than "simple" wind slabs. Fresh slabs will be reactive to your weight and may produce avalanches that break wider and deeper than you might expect. Triggering these avalanches remotely (from a distance above, below, or to the sides of steeper slopes) is a real possibility.

    (2/28/2023) This large avalanche was observed on a N aspect of Copper Mountain near Banner Summit. The crown extends into terrain that is mostly sheltered from the wind.

  • Persistent Slabs

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

    What is it? Layers of weak snow in the upper snowpack can produce wide, destructive 2-3+' thick slab avalanches. Expect to find weak, sugary facets on shaded slopes and crust+facet sandwiches on slopes that face the sun. 

    Where is it? The depth of these weak layers varies from slope to slope, but it's safe to assume that they exist on most slopes. The sensitivity will be amplified in wind-affected terrain in more exposed terrain.  However, enough snow has fallen here that avalanches failing in terrain sheltered from the wind are a real possibility.

    How can you recognize it? Shooting cracks and collapsing are clear signs of an unstable snowpack. Natural and human-triggered avalanches will offer guidance on what type of terrain and slopes these avalanches are likely to be triggered on, but it's safe to assume that they exist on many slopes.  It might take some digging into the snow to reveal previous wind-affected layers that the new snow has masked in more sheltered locations. 

    How can you manage it? Persistent weak layers can fail unpredictably and break significantly wider and deeper than you might expect, producing much larger avalanches. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and what you are connected to in slope steepness. The combination of a recent large natural avalanche, an ugly snowpack structure, and unstable snowpack test scores is plenty of evidence to keep me out of big, steep, complex avalanche terrain.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain points to the potential for encountering avalanche problems outside of areas that are obviously affected by the wind.

Avalanche Discussion

Over the last 48 hours, I have documented at least 50 natural avalanches from Hailey to the Sawtooth and White Cloud mountains. Triggered avalanches have increased as well. They ranged from small to large avalanches and landed on most sides of the compass. Some showed the classic signs of a persistent slab, with crowns extending wide and wrapping through terrain features. All undoubtfully failed on some form of a weak layer, whether it needed the help of wind or not. 

Recent small storms built up a slab over fragile, weak layers that grew in the January and February droughts. The sensitivity of this slab increased with every storm that brought more wind and snow until it met its breaking point. Now that slab is well established across all of the Forecast zones. 

Terrain management becomes crucial to avalanche avoidance when triggering slides are likely. Consider the slopes you are connected to when a persistent slab exists in the snowpack. Traveling on slopes that aren't steep enough to avalanche will significantly reduce your chances of triggering an avalanche. Be hyper-aware of the slopes just steep enough to slide and connected to those lower-angle ones you have your sights playing on. A small pocket of steep terrain can be enough to get snow moving and connect to lower-angle terrain, causing a bigger avalanche. 

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