Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Mon
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Out of date — this forecast expired 7 years ago.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

Dangerous avalanche conditions exist. Widespread unstable conditions were observed in this zone on Friday. Triggering an avalanche remains likely, and sticking to lower-angled slopes remains the best approach. Recognize that you could trigger avalanches from above, to the side, or from below steeper slopes.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Thursday's snowfall and wind added a good thump to an early-season snowpack with several prominent weak layers (read Forecast Discussion below). On Friday, Chris and Ben were near Banner Summit yesterday where they experienced widespread collapsing and cracking of the snowpack. Walking a ridge above steeper terrain produced collapses that remotely triggered several avalanches - these broke 16 inches deep and were more than large enough to bury or injure a person. Yesterday, a number of human-triggered avalanches occurred in neighboring zones with a similar snowpack.

    Given our weak snowpack and the potential for human-triggering, it remains best to stick to lower-angled terrain. Conditions will be most dangerous on upper elevation slopes with evidence of wind drifting. Be alert to signs of unstable snow such as cracking or collapsing—these are obvious indicators you've found dangerous conditions.

Avalanche Discussion

If you're a Cliff Notes type, here's the short story: our forecast area has a complex, early-season snowpack with several prominent weak layers. Thursday's storm produced varying amounts of snow and wind across our area, but natural or triggered avalanches occurred in each of our zones. The most recent of these occurred yesterday, with human-triggered avalanches in the Galena Summit area and in the Salmon Headwaters. Given the likelihood of triggering an avalanche—especially in our northern and western mountains—sticking to lower-angled terrain remains the best approach. Given the possibility of remote-triggering, recognize that you could trigger avalanches from above, to the side, or from below steeper slopes.

If you're ready for the longer story, let's take a closer look at some of the weak layers we're dealing with:

December 7th Surface Hoar:The December 7th storm buried a layer of surface hoar, which can be now found about 12-16 inches deep on many slopes. This layer has been responsible for most of the human-triggered avalanche activity since Thursday's storm, the most recent of which occurred yesterday. Friday on Banner Summit, Ben and I saw every sign of instability in the book: poor snowpack test scores, collapsing and cracking of the snowpack, and natural and remotely-triggered avalanches.

Thanksgiving Storm Snow:Thanksgiving brought some much-needed snowfall, but cold, clear weather following the storm quickly turned this to weak facets. This layer is most prominent in our southerly zones that received the brunt of the Thanksgiving storm, and is less common in our northern mountains that were left out of the Thanksgiving fun. This layer produced some remotely-triggered avalanches in the Eagle Creek drainage following the December 7th storm.

September and October Depth Hoar:The snow that fell in the early fall turned to well-developed facets and depth hoar during our dry November. This layer is most prominent on upper elevation, northerly-facing slopes and in alpine terrain - places where this snow didn't melt during the November drought. This layer is easily-identified—it's the large-grained, sugary snow found near the base of the snowpack. 

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