Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Triggering a 1.5-2 foot thick avalanche remains possible on some slopes. Avalanches are more likely on shady slopes facing E-N-W and could occur in both sheltered and wind-affected terrain. Today's storm will build drifts in terrain that's exposed to the wind. These slabs are likely to be small but could be easy to trigger. 

Problemi valanghivi

  • Persistent Slabs

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

    A layer of surface hoar is buried 1.5-2' deep on many shady (E-N-W) slopes. This zone has had the greatest number of both natural and human-triggered slides attributed to this layer. Sun Valley Heli Ski guides recently observed a natural avalanche in the W Smokys that appears to have involved this weak layer (above/right, details). Since then, observers have continued to find this layer in snowpits, but snowpack tests show signs of improvement.

    Surface hoar is a tricky weak layer. Its patchwork distribution means you may find it on one slope but not the next. Commonly it's found in small clearings and open, wind-protected terrain on shadier aspects (example). In fact, most of the avalanche activity on this layer has occurred in shady, middle-elevation terrain on slopes where signs of wind loading were not obvious. This problem can lurk well below windy ridgetops, waiting to be triggered in steep terrain further downslope than the obvious starting zone.

    You can reduce your risk by avoiding shady slopes (facing E-N-W) that are very steep (greater than about 35 degrees). Consider the consequences of going for a ride. Even small slides can have bad outcomes if they lead to trees, cliffs, or a creek bed.  

    ADDITIONAL DISCUSSION: Older weak layers (often facets found near crusts, with some surface hoar) exist deeper in the snowpack. These layers are buried beneath dense, 3-4+ thick slabs. While triggering them is unlikely, it can't be ruled out in steep, rocky, wind-affected terrain. 

    (1/23/2023) This natural avalanche in the W Smokys likely occurred during the wind event on Jan 22. The depth and characteristics are consistent with the early-January surface hoar layer. It appears to have been triggered by a small wind slab. 8500', E. Sun Valley Heli Ski photo.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Today's storm will build upon a lingering wind slab problem. Additional snow and wind will create thin, new slabs and thicken the hard slabs that already exist. You're most likely to trigger a wind slab at upper elevations, although it's also possible on some wind-exposed middle and lower elevation slopes.  N and NW wind often make a mess of the Sawtooths. They can create alternating patterns of wind erosion and slabs across cirques and basins and blow straight up couloirs forming wind slabs in unexpected locations.

    Wind slabs can often have a "chalky" appearance (photo). They can feel hollow or drum-like, which indicates that they are sitting atop weaker snow and should be avoided when on a steep slope. Cracking and collapsing are clear signs that you've found a sensitive slab. While I expect slabs to be fairly small, they could easily knock you off your feet, strain you through trees or bury you in a depression (photo). 

    (1/24/2023) Recent northerly winds formed hard wind slabs up to a foot thick at exposed ridgelines near 9000' on Fox Peak. The fresh slabs were difficult to trigger, but Scott was able to get one to crack about 20 feet out from his skis. The slabs only extended 10-30 feet below the ridges, but the slabs' hollow sound and feel was "creepy".

Avalanche Discussion

The avalanche danger is MODERATE across the forecast area. At first glance, avalanche conditions may look similar, but there are variable and divergent conditions across our region. No two MODERATE dangers are alike, and we've arrived at this danger level for different reasons. If you recreate in multiple portions of our forecast area, all of this can be hard to keep track of. To simplify matters a bit, I think it's helpful to mentally separate the deeper snowpacks of the northern and western mountains from the shallower snowpacks of the southern and eastern mountains:

  • The snowpacks in the Sawtooths & W Smokys and Banner Summit zones are more uniformly deep. The deeper snow is advantageous, as it helps to reduce the odds of triggering an avalanche on deeper weak layers buried in December and November. The weight of the overlying slab has helped these older layers to heal, and the stiff snow above them means they're harder to impact. On the flip side, snow since the start of January has buried a weak layer of surface hoar beneath a stout 1.5-2' thick slab on slopes that face E-N-W. The majority of the recent persistent slab avalanches occurred on this layer.
  • The Galena Summit & E Mtns zone has a variable and complex snowpack. The early January surface hoar can be found buried 1-1.5' deep, but it didn't get quite enough load to be a widespread issue. The surface hoar layer remains more problematic where recent or past wind loading has created a stiffer slab in the upper snowpack. Although the surface hoar is less concerning in this zone, the older, more deeply buried weak layers are more worrisome. With a shallower snowpack than further north and west, and more rocky, wind-affected alpine terrain, there are more areas where these weak layers are closer to the surface.
  • The Soldier & Wood River Valley zone can be split in two. In the mountains above Ketchum and Hailey, plenty of weak snow exists but a strong slab is less common. You can avoid most avalanche hazard by staying off of wind-affected slopes where a stiffer snow surface exists. In the western portions of this zone, including the Soldiers and the mountains around Dollarhide Summit, a deeper and much more complex snowpack exists (video). Avalanches occurred in the Soldiers on the early January surface hoar layer, and deeper weak layers may remain a concern in rockier, wind-affected alpine terrain.  

This season has been hard. Plagued with persistent weak layers, it's been an exercise in patience. When I take a step back and think of the big picture, I can't help but see the complexity and variability out there. This gives me much less confidence in choosing a safe place to play. When faced with uncertainty, the prudent move is to stick to inherently safer terrain. This includes slopes less than about 35 degrees and those with more favorable outcomes in case I get surprised.

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