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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist. Human-triggered avalanches involving 1-3 foot thick slabs of dense, wind-blown snow are likely. Triggered avalanches can step down to deeper weak layers, producing very large, very destructive avalanches. You can reduce, but not eliminate your risk by steering clear of areas that have been recently loaded by the wind.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Friday's storm brought 18-24" of snow (1.5-1.8" of SWE) to this zone. Snowfall was accompanied by moderate to strong winds blowing out of the SE-S-SW. This combination built dense, 1-3 foot thick wind slabs on many slopes. Triggering a wind slab avalanche large enough to bury you remains likely today.

    You're most likely to find a reactive slab in upper elevation terrain. Wind slabs commonly form along ridgelines and near mid-slope terrain features like ribs and gullies. The wind was blowing more strongly than it typically does in this zone so you may find sensitive wind slabs extending down into middle elevations as well.

    Wind slabs and cornices that fail can be very effective triggers for the destructive persistent slab avalanches described below in Problem 2. 

    (3/10/2023) This very large slab avalanche failed in a heavily wind loaded location on a NW-facing slopeat 6,800' above Croy Canyon. Large amounts of snow are being transported in this photo.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2.5–3

    Weak layers are buried underneath dense, 2-4 foot thick slabs of snow in this zone. This combination can produce very large avalanches capable of destroying a house. If you dig down, you'll find facet+crust combinations on slopes that face the sun and thicker stacks of weak facets on shaded slopes. These weak layers were acting up and producing large avalanches before Friday's storm (photo at right/above).

    Avalanches that fail on these layers can break very wide, wrapping around multiple aspects and connecting multiple avalanche paths. These slides can run the length of the avalanche path, impacting flat terrain long distances away from steeper slopes. 

    Managing persistent slab problems is difficult. If you want to completely eliminate the risk of triggering one of these beasts you'll have to avoid avalanche terrain. You can reduce (but not eliminate) your risk by choosing gentler slopes that are sheltered from the effects of the wind. And don't forget to pay attention to what is above you, these avalanches can be triggered from long distances away from steeper slopes. 

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain is an excellent example of a slope that did not need wind loading to become unstable. 

Avalanche Discussion

Friday's storm produced a truly impressive cycle of natural avalanches (video here). Avalanche activity was much most pronounced in our Galena Summit and Eastern Mtns and Soldier and Wood River Valley Mtns forecast zones. Head over to our Avalanche Database (map, list) to browse through some of these, we've entered about 200 avalanches large enough to bury you that occurred since Friday. Notable avalanches include slides on Della and Carbonate Mountains west of Hailey that dammed the Big Wood River (photo here) and hit several houses (photo here). We observed a number of very large natural avalanches in the Boulder and Smoky Mountains that broke thousands of feet wide (photo here). Natural avalanche activity was most widespread on Friday, though Scott observed 5 large natural avalanches that released in the Wood River Valley yesterday as well (observation here).

The Avalanche Warnings have expired, but conditions remain dangerous. Avalanche accidents commonly occur during the period of decreasing danger following major loading events. This is exactly where we find ourselves today. The mountains may not be crashing down like they did on Friday, but that doesn't mean it's time to let your guard down. Human-triggered avalanches remain likely, and the slides you trigger will not be small. Spend a few minutes browsing through the Avalanche Database to get a sense for the types of avalanches you might see and/or trigger out there. 

I recommend you head into the mountains with a conservative mindset today. If you are dead set on entering avalanche terrain, choose terrain where the consequences of being caught in an avalanche are lower. Your likelihood of surviving an encounter with an avalanche is greater in terrain free of terrain traps (creek bottoms, trees, rocks). If you just want to be outside in the mountains and come home safely tonight there are lots of great options; the skiing and riding are excellent in low angle terrain right now. 

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