Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanche conditions remain dangerous. Significant amounts of snowfall and wind over the past week have deeply buried weak layers beneath 3-5 feet of dense snow. Numerous very large and destructive avalanches occurred naturally during the storm—triggering one of these beasts would have catastrophic results. Sticking to lower angled terrain is the best way to reduce your risk.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Last week's extended storm cycle heavily favored our western and especially northern mountains. To say that Banner Summit got clobbered is an understatement. This area likely received nearly 4 feet of new snow since last weekend. Our persistent weak layers are now buried around 3 feet at middle elevations and beneath a 4-5+ foot thick dense slab at upper elevations (see photo). The nature of this new avalanche problem was evident when the storm first cleared on Wednesday, revealing numerous deep, destructive avalanches on Copper Mountain and the ridge extending south (see photo at right and in Media).

    As we learned last year, when persistent weak layers become deeply buried beneath a dense slab, it presents a tricky scenario. Avalanches become harder to trigger, but the resulting slide would be catastrophic. These weak layers may be more easily impacted by your weight at mid-elevations where the slab is thinner, or in rocky and/or wind-affected areas where there are shallower areas. Observations since the storm ended are still fairly limited, and there's a high level of uncertainty with the state of the snowpack in this zone. But one thing is for sure—you don't want to tangle with one of these avalanches. To reduce your risk, stick to lower slope angles and low consequence terrain.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    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 is intertwined with the persistent slab problem. Wind loaded slopes will have even more weight on the buried weak layers, and wind-affected areas are likely to have thinner spots where you can more easily impact these deeper layers.

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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