Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Avalanche Danger will rise to HIGH. Wet snow avalanches will be easy to trigger and run naturally on slopes receiving direct sun as we enter day 6 of an intense warmup. These slides can become large and destructive and break down deeper in the snowpack. On colder, drier slopes, avalanches that break on buried weak layers remain a worrisome possibility. Both of these types of slides are likely to be unsurvivable if you find yourself caught in one. Today is a day to stay off of and out from under steep, sunny slopes.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2.5

    WET LOOSE avalanches will be easy to trigger and will run naturally as the sun melts the weak crust on the snow surface. Though these slides start small, expect to see them become large and destructive as they run downslope. If you are on a steep slope with mushy snow at the surface, triggering one of these slides is likely. Natural slides often start in rocky terrain or near trees pushing heat into the snowpack. Meltwater has penetrated deeply into the snowpack, and many of these slides will gouge through and entrain this wet snow. The result is a slide that moves the entire snowpack (and maybe some rocks and trees) downhill in one wet, scary mess.

    Large CORNICES overhang many slopes. These are weakening with high temperatures and failing. Remember to both give these beasts wide berths while traveling on ridgelines and be aware of the overhead hazards they pose. Falling cornices also will be effective triggers for larger, more destructive avalanches on the slopes below. 

    Pay attention to what is above you. These slides will be releasing naturally. Today is not the day to linger under slopes that are soaking in the sun.

  • Wet Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Yesterday, Ben remotely triggered a destructive wet slab avalanche near Senate Peak. Two days ago he triggered a larger slide near Dollarhide Summit by throwing a snowball at a slope (see photo at right/above). That afternoon, I watched 3 wet slab avalanches run naturally from the top of Galena Peak.

    Meltwater percolating through the snowpack is weakening the bonds at buried persistent weak layers. When this happens, wet slab avalanches are on the menu. These are most likely during the heat of the day and into the late afternoon, but the timing of these types of slides is unpredictable. Even slopes with a refrozen crust at the surface are suspect when water is moving through the snowpack. Natural avalanche activity can also continue long after the heat of the day. 

    Smaller wet loose slides can trigger much larger wet slides as they travel downslope. If you trigger one of these slides it will be nearly impossible to ski or ride out of. Before the end of the day, I expect to see destructive wet slab avalanches running naturally. These have the potential to run full track, depositing deep piles of debris on the valley bottom.

    (3/17/2024)

    This large wet slab avalanche was triggered on Sunday when Ben threw a snowball at the slope. It ran 1,400' to the valley below. 

    Photo: Ben VandenBos

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    If you head to cold slopes to seek out dry snow you will still have avalanche problems to manage. In these areas, triggering a wide, destructive avalanche that breaks on widespread buried weak layers remains possible. These weak layers have been slowly gaining strength, but they haven't gone away. If you dig down you'll find crusts with facets here on sunny slopes, and facets without crusts on shaded slopes.

    Triggering an avalanche involving this snow is most likely in steep, rocky, wind-swept terrain where the snowpack is variable and you can find thinner spots in the overlying slab. However, the skier-triggered persistent slab avalanche that failed in a steep couloir in the Sawtooths proves these are a real concern even in areas that typically host deeper snowpacks. The first sign of instability involving these layers will be the massive avalanche that you trigger.  There is no good outcome to being caught in a slide like this. 

    (3/6/2024) Very large avalanche on a SE aspect above Window Lake north of Boulder Basin. Photo: Sun Valley Heli Ski

Avalanche Discussion

Forecasting can seem like a colossal undertaking. However, as a mentor has told me many times, what our jobs boil down to is trying to describe the world that you all are about to step out into the best we can. This includes talking about what we know, and acknowledging uncertainty in the things we don't so you can build in safety margins to your travel plans. This job becomes a lot more simple when you focus more on painting an accurate picture of what is going on in the mountains rather than getting all the colors, boxes, and sliders "right". Let's talk about what we know and where our uncertainty lies.

Wet slab avalanches are inherently unpredictable. We are certain that meltwater has been percolating through the snowpack without solidly refreezing for multiple nights. We know this meltwater is pooling around weak layers, and saturating and changing the properties of our slabs. Wet slabs naturally release when these impacts reach a tipping point. Each day of sustained weather like we've been experiencing pushes us closer to that tipping point. But if today will be the day that we reach it is almost impossible to say. I would be equally unsurprised today if we saw a widespread large wet slab cycle in the Boulder Mountains, or saw little new natural wet slab activity at all. 

So, what does this mean for you as you step out into the mountains today? The snowpack starts with a crust this morning and will break down quickly. After this quick shift, wet loose avalanches can start anywhere the snow is moist and mushy. While it's hard to speak to how likely natural wet slab avalanches will be today, by the afternoon I can say with some confidence that human-triggered wet avalanches will be very likely. If you are on a steep slope during the heat of the day or after, triggering a large destructive slide is on the menu for you — Ben proved this by intentionally triggering several wet slabs in the Boulders yesterday evening, one from 15 feet away. Wet loose slides can start at a point, gain speed and mass as they move downhill, and then flank out to create these large and destructive wet slab slides. If you head to colder, drier aspects to avoid wet snow issues, you'll still find a persistent slab problem that has added complexity due to meltwater potentially reaching these weak layers as well. 

Overlapping complex problems, as well as the hard-to-predict nature of both wet slab and persistent slab problems makes for a tricky day to travel in the mountains. If you've made it this far in the season, you've been patiently navigating persistent slab and new snow issues.  Hold on to that patience just a bit longer, and make conservative travel choices. I've stepped back considerably from the terrain I was entering a week ago, and will continue to do so until I can reevaluate after the warmup is over and we get a solid refreeze. Today is the day to start early, end early, stay off of and out from under steep slopes, and mostly just stay out of the way. 

Régions couvertes