Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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1 · Debole
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In sintesi

On slopes with the best skiing and riding conditions—those with lots of soft, fluffy powder—you are unlikely to trigger avalanches. Triggering avalanches is possible on slopes with wind drifts or stiffer snow at or near the surface. There, you may be able to trigger small slides involving only the recently drifted snow or large avalanches that fail on weak snow lower in the snowpack.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    The persistent slab avalanche problem is not widespread in this zone, but there are two scenarios to consider when planning your day in the mountains:

    1. Old October snow near the ground: This layer of grey, crumbly facets is buried 2-4 feet deep on some shady middle and upper elevation slopes. This layer has plagued us all season and is now less worrisome, but it is keeping avalanche professionals leery of very steep alpine terrain.
    2. Crust + facets below the recent storm snow: This less obvious layer may exist on very steep (35-45*) slopes facing SW-S-SE. Several 2-3 foot thick, natural avalanches failed on this layer in neighboring zones during the last storm. 

    Where are you most likely to trigger avalanches on these layers? Where you can check most of these boxes:

    • "Prime time" slope angles around 35-45* in steepness
    • Wind-loaded slopes, or slopes where wind created hard or stiff layers in the upper snowpack
    • Rocky slopes with variable snowpack depths—its easier to trigger avalanches in places where the weak layer is 1-2 feet below the surface

    Avoid terrain where you check all of the boxes above to reduce the chances of triggering large, persistent slab slides. 

    (1/3/2022) This large persistent slab avalanche was observed above the East Fork of the Big Wood River prior to the recent storm. It failed on facets (October snow) buried near the base of the snowpack.

  • Wind Slabs

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

    Soldier Mountain Cat Ski staff triggered a sizeable avalanche with explosives on Monday (photo). Wind slabs have become less sensitive to triggering in recent days, but you may be able to trigger similar slides in obviously wind-loaded terrain. Slabs are largest and most widespread at upper elevations, especially in the Soldier Mtns and near Dollarhide Summit.

    Fortunately, this avalanche problem is easily managed; avoid exposed, 35-45* slopes with large drifts, dunes, or ripples on the surface. Some other tell-tale signs of wind loading or wind slabs:

    • Cracks shooting out from your boards or skis
    • You or your sled stay on top of a firm, supportable snow surface
    • The snow sounds or feels hollow or "drummy"

    Perhaps the most important reason to avoid obviously wind-loaded terrain: the slabs may have formed above the weak, faceted snow described above in Problem 1. Very steep slopes with both buried persistent weak layers and wind-loading are the most likely places to find trouble today. 

    (1/11/2022) This wind slab avalanche was triggered with explosives during avalanche control work on 1/10/22 by Soldier Mountain Cat Skiing staff. E-ESE facing slope at 9,300'.

Avalanche Discussion

EVALUATING 'RETIREMENT-AGED' FACETED WEAK LAYERS

The layer of faceted snow found near the ground on many upper and middle elevation shady aspects (NW-N-NE-E) and some upper elevation sunnier aspects has experienced a lot in its brief career; three abnormally large, multi-day storms in less than a month. How is it aging?

  • Less, and generally smaller, natural avalanche activity with each successive storm
  • No recent remote triggered avalanches
  • Reports of large snowpack collapses are now infrequent
  • Improving but still somewhat inconclusive snowpack test scores
  • Getting physically "shorter" - mechanical compression is making the layer thinner where the slab above it is more than a few feet thick

As weak layers—and people—age, they tend to mellow. The faceted, old October snow is obviously "mellowing". The million-dollar question: is it ready to ride off into the sunset and retire? 

  • Where deeply buried (4-8 feet): Observations and experience indicate you would have to be unlucky to trigger a huge, destructive avalanche on this layer. However, I like using a "7-day stopwatch" before I start to consider entering the dragon's lair: prime-time 35-45* slope angles in shady, rocky, alpine terrain where the snow depths are variable. Because the problem is almost impossible to accurately evaluate on a slope-specific scale, I wait a minimum of 7 days from the last loading event before I consider entering terrain where a proven performer like this weak layer exists. 
  • Where buried 2-4 feet deep: Many local professionals (me included) continue to avoid wind-affected, prime time 35-45* slopes angles where this weak layer exists. These slopes are the most-likely locations to trigger large avalanches within our Forecast area. 

What's the moral of the story? Triggering a large, destructive avalanche is now unlikely but is still on the table. Unfortunately, it's a lot easier to predict how this type of layer will behave on individual slopes when it is younger (during the first couple of big storms) than it is now. We are thinking about the October facets' obituary and may be able to write it in the coming days and weeks, but we're not writing it today.

An update on the "new employee": The crust and facet combination buried underneath last week's storm snow on some steep, sunny aspects (SW-S-SE) produced several 2-4 foot thick avalanches during the storm. My hunch is that it may be considering an early buyout package and retiring at a young age, but it's too soon to tell. For now, we have to assume this recent hire is punched in and still in need of supervision. 

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