Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Natural and human-triggered avalanches large enough to bury people are very likely to occur. Some will be large enough to snap trees or destroy a wood-frame house. Avalanches can be triggered from long distances away from steeper slopes. Avoid all avalanche terrain—stay off and out from below slopes steeper than about 30 degrees.

The backcountry AVALANCHE WARNING does not apply to the HWY 21 avalanche program. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–3

    We're facing two distinct types of Persistent Slab avalanches:

    1. Expect natural and human-triggered, 1-3 foot thick slides involving the snow from the past week on both sheltered and wind-loaded slopes. Assume this problem exists on all upper and middle elevation slopes and on shadier, lower elevation aspects. These avalanches will be large enough to bury people. Although the slides will be largest in wind-loaded terrain, you can encounter this problem on all steep slopes, including those sheltered from the wind.
    2. The avalanches described above can "step down" to weak snow near the ground, producing huge, unsurvivable avalanches. This weak snow layer exists on all upper and most shaded middle-elevation slopes (W-N-E). 

    Avoidance is the only way to stay out of harm's way. Some slopes will release naturally; many others are primed and ready to be triggered. You'll need to avoid the runouts of large avalanche paths and consider your proximity to overhead hazards. These slides can be triggered from a distance, including flat terrain near the base of steep slopes. 

    (1/13/2024) This set of large avalanches was observed in the Banner Summit Zone, south of Copper Mtn. These crowns span over 1,000' of terrain and are an estimated 2-3 feet thick. Slightly older avalanches are visible on the left side of the image.  It is unknown which weak layer these slides failed on.

  • Wind Slabs

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

    While the Persistent Slabs described above are by far the biggest concern, natural and human-triggered Wind Slab avalanches big enough to bury people are very likely. These slides and relatively small loose snow sluffs can trigger the much larger Persistent Slabs described above. 

Avalanche Discussion

Last night's storm delivered another hefty load of storm snow. Mild temperatures made the snow top-heavy, a characteristic that will be exacerbated with warm sun and mild temperatures again today. While fresh slabs are most likely in wind-blown areas, you should expect to find fresh, sensitive slabs in sheltered terrain where 24-hour storm totals approach or exceed a foot.

All this action at the surface is happening above two ugly, well-defined persistent weak layers. Check out Ben's video for a great review of these layers and the avalanches they produced during last week's storm. Weak layers like these are rarely one-trick ponies. Expect to see fresh crowns this morning and anticipate natural avalanche activity throughout the day. 

Today's a day to make the simple choice to stay out of avalanche terrain. Unfortunately, that is easier said than done. Much of the terrain we consider "safe" at lower hazard should be off the table. If you decide to head into the mountains, recognize that avalanches can release naturally and be triggered from flat terrain a long distance from the slope. This means they may break well above you while descending or at the bottom of a slope. 

Enjoy the fresh snow, but widen those safety margins. Re-think your "safe" routes. Recent slides crossed common snowmobile trails and have pulled back into relatively flat terrain above steeper slopes.  Ask yourself, how far will that path run? How close am I to the edge?

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