Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Avalanche conditions are still dangerous. Triggering a 2-3' thick avalanche is likely on most slopes—especially in wind-drifted terrain. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    We have a well-established persistent slab problem across the entire forecast area. The problem has been slowly building since the weak facet layer was buried over a month ago. Each storm has produced a new round of avalanche activity, but the snowfall and strong winds from last week caused an impressive number of very large avalanches in this zone. The loading from the recent storm was enough to release large slab avalanches in the Sawtooths (observation, video) and the Smoky Mountains (observation, observation). Avalanches occurred on many different aspects, in both obviously wind-loaded and generally sheltered terrain. 

    The December facet layer is buried about 2-3' deep on almost every slope. It's can be felt with a ski pole and is very obvious in snowpits. Often there is a high degree of uncertainty surrounding persistent slab problems. Now is not one of those times. Conditions remain dangerous and it's likely you'd trigger a large avalanche if you ventured onto a steep slope. Providing proof that the snowpack remains touchy, Soldier Mountain Cat Ski guides remotely-triggered an avalanche in the Soldiers yesterday.

    The best—and often only—way to manage the persistent slab problem is by sticking to lower-angled terrain. Given the possibility of remote-triggering, you'll also want to avoid being below steep slopes. 

    (1/13/2021) This very large avalanche occurred on Cabin Peak, just north of the Alturas drainage, during the intense storm on 1/12-1/13.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Strong winds this past week ravaged the snowpack. It formed touchy wind slabs on many exposed slopes, and the added weight of windblown snow contributed to many natural avalanches. Yesterday's few inches of new snow combined with moderate winds may have created a fresh batch of small wind drifts at upper elevations. 

    Although triggering a wind slab will be less likely today, it's tough to separate the wind slab problem from the persistent slab problem described above. Wind-transported snow has added stress to the buried weak layer making wind-loaded slopes more dangerous, and if you triggered a wind slab, it could "step down", failing on layers deeper in the snowpack and becoming much larger than the initial avalanche. 

    Wednesday and Thursday's strong to extreme wind built fresh wind slabs on many slopes.

Avalanche Discussion

While the December facet layer exists nearly everywhere, the slab overlying the weak layer is anything but uniform. In fact, it's interesting to look at how the slab and weak layer vary across the forecast area as it illustrates nearly the full life cycle of a persistent slab problem.

Formative Years. The Wood River Valley has received the least amount of loading on the weak layer, and the slab is very soft and only about a foot thick. There isn't quite enough slab to produce widespread instability—the important exception being in wind-loaded terrain.

Troubled Teenager. In the western portion of the Solder & Wood River Valley zone, and the entire Galena Summit & E Mtns zone, it took nearly a month but the slab has matured into 2' of fairly dense snow. It has the growing pains to prove it—the storm last week pushed the snowpack into a tailspin of avalanche activity. This part of the forecast area is particularly dangerous—a 2' thick slab is the "perfect" combination of human-triggerability and dangerous consequences.

Fully Mature. In the Sawtooths & Western Smokys, the slab depth increases to 2-3' and becomes even denser. Last week's storm produced a number of large to very large avalanches—several could have destroyed vehicles or a house. As the slab becomes increasingly thick and dense, avalanches become harder to trigger. But if you do trigger one, it's likely to be unsurvivable.

A Few Gray Hairs. The Banner Summit zone has the meatiest slab of our forecast area and is 3+' thick in many places. This part of the forecast area had less natural avalanche activity following last week's storm, and the weak layer is starting to show early signs of getting "squashed" beneath the weight of the slab. But don't mistake being middle-aged for past its prime—this deep slab problem may have gained some tolerance with time, but getting on its bad side will have disastrous consequences. 

RIP. Sorry, this is likely a long ways off!

Be sure to check out Ethan's latest Weekend Update. Spoiler alert—it was yet ANOTHER exciting week!

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