Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Dangerous avalanche conditions exist. Human-triggered avalanches involving dense, 1-4 foot thick slabs of snow are likely. Avalanches may be very large and destructive and can be triggered from long distances away from steeper slopes. Conservative terrain selection is encouraged today.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2.5–3.5

    Friday's storm brought 12-24" of snow (1.1-1.8" of SWE) to this zone. The rapid loading pushed the layers of weak snow now buried in the upper 2-4 feet of the snowpack past their breaking points. Yesterday in my travels, I observed dozens of avalanches that were large enough to destroy a house, including the slide pictured at right/above. This avalanche broke over 3,000' wide, or nearly 10 football fields laid end to end. Pause for a moment and think about that.

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

    The only way to manage this problem is to avoid avalanche terrain and terrain exposed to overhead hazard. This includes meadows that are well away from the base of any steep slope. You can trigger an avalanche that fails thousands of feet above you from flat terrain at the valley bottom.

    (3/11/2023) This very large persistent slab avalanche was observed in the Boulder Mountains. It failed over 3,000' wide, wrapping around SE-E-NE aspects between 10,000' and 10,800'.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    Friday's storm was accompanied by strong winds blowing out of the SE-S-SW. The combination of new snow and wind built very large, dense, 1-3 foot thick wind slabs on many slopes. Triggering a wind slab avalanche large enough to bury you is likely today.

    Wind slabs will be largest and most broadly distributed in upper and middle elevation terrain. Wind slabs commonly form along ridgelines and near mid-slope terrain features like ribs and gullies. Thanks to the strength of the wind and the amount of new snow available for transport, these slabs stretch down into low elevation terrain as well. Typical locations for lower elevation wind slabs in this zone are in the foothills of the Boulder Mountains and in the foothills of the White Cloud Mountains, east of Hwy 75.

    Wind slabs and cornices that fail can be very effective triggers for the destructive persistent slab avalanches described above in Problem 1. 

    (3/11/2023) These avalacnhes failed in heavily wind-loaded terrain in the Boulder Mountains. They failed on a SE-facing slope at 9,600'. Note the obvious dunes visible in the snow surface above the crown.

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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