Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Sun
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3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Avalanche conditions remain dangerous. Weak layers buried 2-3 feet deep have been stressed by last week's nearly continuous snowfall and wind. You are most likely to trigger an avalanche on slopes with evidence of wind drifted snow, but triggering a slide in sheltered terrain is also a possibility. Choosing gentler terrain and avoiding slopes with evidence of wind are the best way to reduce your risk.

Problemi valanghivi

  • Persistent Slabs

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

    Last week's snowfall and wind added a significant amount of new load to the snowpack—especially in the Soldier Mountains— and our persistent weak layers are now buried 2-3 feet deep. While less natural activity occurred in this zone compared to further north, several significant slides were observed—including these large ones on Peak 1 in the Soldiers.

    The persistent slab problem is intertwined with the wind slab problem discussed below. You’re most likely to trigger a persistent slab avalanche where a stiff, wind-loaded slab sits over these weak layers. This is especially the case in the Wood River Valley, where less snow fell last week and any sort of slab is uncommon outside of wind-affected areas. On Thursday, we found this snow structure during our site investigation of the fatal avalanche that occurred Wednesday in Baker Creek. Given the nature of our weak layers, it's important to know that slides may be triggered remotely—from gentle terrain above, beneath, or to the sides of steeper slopes.

  • Wind Slabs

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

    Last week's stormy weather brought nearly as much wind as snow, but the winds finally eased a bit yesterday and especially overnight. Wind slabs today will likely be smaller and less reactive to the weight of a skier or rider. But continue to watch for and avoid wind drifted slopes as there may be a few lingering problems out there. It also pays to recognize that the wind slab problem goes hand-in-hand with the persistent slab problem described above. Many wind loaded slopes will have a stiff, dense slab of snow sitting atop the buried weak layers. Thursday night, the groomer on Couch Summit in the Soldiers reported several fresh slides matching this scenario—see the photo at right

Avalanche Discussion

Last week's extended storm cycle heavily favored our western and especially northern mountains. To say that the Sawtooths, Banner Summit, and Western Smokys got clobbered is an understatement. The Soldiers also received a significant amount of new snow, while less fell in the Galena Summit area, our Eastern Mountains, and the Wood River Valley.

As the dust settles, it's time to make sense of our new world. While much of our area has similar persistent weak layers, they're now buried under widely varying amounts of snow. Although a conservative mindset and terrain choices are the name of the game throughout our area, it's still important to understand the nature of the snowpack you're recreating in.

  1. Shallower areas: Wood River Valley. In this area, there is no shortage of weak snow, but many slopes lack a cohesive slab. Conditions are most dangerous where recent or previous wind events have created dense drifts atop this weak snow. 
  2. Moderately deep areas: Galena Summit & Eastern Mountains. Persistent weak layers in this zone are buried 2-3 feet deep. You are most likely to trigger a slide where the wind has added additional load and stiffness to the overlying slab. This was the case in the tragic avalanche fatality that occurred in Baker Creek on Wednesday. Avalanches are less likely but still possible on wind-sheltered slopes.
  3. Deep areas: Western Smokys, Sawtooths, and Banner Summit. These mountains received the lion's share of last week's snowfall, and the same weak layers that exist elsewhere are now buried by 3 to 5 feet of dense snow. Deeply buried weak layers are difficult to assess and present a high level of uncertainty. Slides are more difficult to trigger but will have dire consequences.

Details from Wednesday's Avalanche Accident in Baker Creek:On January 15th, 2020, a snowmobiler was caught and killed in an avalanche in the Baker Creek drainage, approximately a half-mile northeast of Baker Lake. We visited the site Thursday to collect data on the avalanche. This video contains preliminary information collected during the site investigation; a full accident report will be published soon.

The avalanche released at an elevation of 9200 feet on a south-facing, wind-loaded slope. The slab broke 2-3 feet deep, 250-300 feet wide, and ran just over 600 vertical feet. The slope angle of the start zone was around 33 degrees, but the slope steepened significantly below the fracture line. The avalanche was triggered from lower on the slope, well below the crown line of the avalanche, and released on a persistent weak layer of faceted snow in the middle to lower snowpack. The avalanche debris range from 3-8 feet deep.

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