Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Wet snow avalanches will be easy to trigger and run naturally on slopes receiving direct sun as we enter day 5 of an intense warmup. These slides can become large and destructive, flanking out widely and breaking 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.

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    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.

    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

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Yesterday, Ben triggered a destructive wet slab avalanche 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. While these events were in zones with shallower snowpacks, the potential for these same slides to run the Banner Summit zone remains. 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

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    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 (see adjacent photo). 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. 

    (3/14/2024)

    This large avalanche was triggered on ascent as three people booted up the final 20' to the saddle at the top. No one was caught. The avalanche broke 2-4+ feet deep on faceted snow. Sawtooth Mtns, N @ 9,900'.

Avalanche Discussion

Yesterday was warm, wet, weird, and wild out in the mountains. Today will be warmer, wetter, weirder, and wilder. Expect wet snow problems to be larger, more dangerous, and more unpredictable today than yesterday. Even on colder slopes, you still can't write off triggering a persistent slab avalanche on buried weak layers. Does this sound hard to navigate? It is.  

The snowpack starts with a crust today, and will break down quickly. After this, wet loose avalanches can start anywhere where the snow is moist and mushy. Hard to predict wet slab avalanches can break on slopes even where surfaces still have a crust, as meltwater from past days percolates through the snowpack to weaken bonds between buried weak layers. 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. All of this will be happening naturally. If you head to colder, drier aspects to avoid wet snow issues, you'll still find a persistent slab problem. 

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. You've made it this far in the season, you've been patiently navigating persistent slab and new snow issues. Things will continue to get more dangerous as we continue into our warmup. Hold onto that patience just a bit longer, and make conservative travel choices. 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. 

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