Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
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2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Numerous human-triggered avalanches occurred this weekend, breaking on weak layers buried 1-2' deep. You're more likely to trigger an avalanche on wind-loaded slopes, but it's also possible in steep, wind-sheltered terrain. Avoid obviously wind-affected slopes and choose lower-angled terrain to reduce your risk.

Problemi valanghivi

  • Wind Slabs

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

    We're a few days out from recent wind events, and most wind slabs have likely stabilized. However, a few could remain sensitive to your weight—especially where they sit atop persistent weak layers (see Problem 1). Look for these slabs near ridgelines and in mid-slope terrain features like gullies. Pay attention to how deep and how dense the snow you are traveling in is. If the snow depth and density increase you are likely traveling through a wind-loaded area. Cracks shooting out from your skis or machine clearly indicate that you've found an unstable wind slab. 

  • Persistent Slabs

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

    Ten human-triggered avalanches occurred during the past week, including at least seven this past weekend (read more in the Forecast Discussion below). Most of these broke 1-2' thick on persistent weak layers buried during the first week of January. Surface hoar seems to be the most common culprit, but facets and/or crusts may also be present. Also, most of these avalanches occurred in middle elevation terrain on slopes where signs of wind loading were not obvious. While none of these were "huge" slides, around half of them were large enough to bury or injure people, and all were capable of carrying someone into a gully, through trees, or over cliffs.

    While these persistent weak layers are slowly gaining strength and triggering a slide is less likely than it was this weekend, they are still capable of producing avalanches. Surface hoar is a particularly sneaky weak layer—definitely not one to be underestimated! Wind-loaded areas will be slowest to stabilize, but you could also trigger persistent slab avalanches on very steep (>35 degree), wind-sheltered slopes. Avalanches can also be remotely triggered from gentler terrain above, below, and to the sides of steeper slopes. Reduce your risk by sticking to less steep terrain and avoiding slopes with terrain traps in the runout zones.

    ADDITIONAL DISCUSSION: In addition to the persistent weak layers in the top few feet of the snowpack, there are more deeply buried layers to keep on your radar. These facets (often above or below crusts) are buried beneath dense, 2-4+ thick slabs—making them difficult to trigger but capable of producing very dangerous avalanches. While triggering them is unlikely, it can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. 

    (1/15/2023) This avalanche was triggered by a snowmobiler in upper Stanley Lake Cr. at the very northern end of the Sawtooths. The rider managed to get off the slab and was not caught. The slide likely released on a persistent weak layer that buried in early January. 8000', NE.

Avalanche Discussion

SURFACE HOARStorms during the first week of January buried new persistent weak layers across much of the forecast area. These weak layers consist of surface hoar on many slopes but facets and occasionally crusts have also been reported. See the Media Gallery below for a few photos of the surface hoar in snowpits. The first avalanches we observed on these new weak layers occurred about a week ago on Galena Summit and also on Banner Summit. Since then, we've built a 1-2' thick slab atop these weak layers and there have been a number of avalanches—culminating in at least seven human-triggered slides this past weekend.

Here is a list of the avalanche activity over the past week, including links to more details where available:

  1. Jan 15 - Stanley Lake Creek - N Sawtooths
  2. Jan 15 - Fishhook Drainage - Sawtooths
  3. Jan 15 - Peak 2 - Soldiers - 2 slides
  4. Jan 14 - Smiley Cr - W Smokys
  5. Jan 14 - Pole Cr - White Clouds
  6. Jan 14 - Peak 2 - Soldiers
  7. Jan 11 - Soldier Cr - Soldiers
  8. Jan 11 - Governors Punch Bowl - Galena Summit - 2 slides
  9. Jan 10 - Camp Cr - Galena Summit

Surface hoar can be a particularly sneaky weak layer—possibly even more so for us since we're much more used to facet layers. It's extremely fragile while on the snowpack surface prior to burial. Wind can easily topple it over, and surface hoar wilts at the first kiss of sun. As a result, it can often be spotty in its distribution when buried—one slope may have it, while another may not. The "classic" terrain for preserving surface hoar is shady and sheltered slopes because they are protected from both wind and sun. Think of middle elevation, open slopes surrounded by trees. While we've found this particular layer of surface hoar in a variety of terrain (including wind-exposed slopes), many of the avalanches listed occurred in terrain that matches the common pattern for areas that harbor surface hoar.

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