Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

You can trigger a 10-16 inch thick slab avalanche today, particularly where recent wind loading has added weight to buried weak layers. Limit your exposure to this problem by sticking to gentler terrain not threatened from avalanche hazard from above. Generally safe conditions exist at lower elevations where the snowpack was soaked by last week's rain and is now frozen solid. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The extended drought in January and February was interspersed with periodic snowfall in this zone. This pattern created a series of weak layers that are now buried 10-16" beneath the snow surface. These weak layers reached the tipping point during last week's storm and a natural avalanche cycle occurred in this zone (observation and photos here). The type of weak snow responsible for these slides can take a long time to heal and triggering an avalanche involving this weak snow remains a concerning possibility today. 

    Where will you find these layers? That's the tricky part. Their character varies from slope to slope and with changes in elevation. I spent 4 days last week looking for these layers in this Zone and got mixed results. In some places they returned unstable snowpack scores, in others they didn't. In some areas they produced widespread avalanche activity and in others they didn't. Digging a snowpit on every steep slope you want to play on is neither practical nor safe. The best approach is to take a step back and choose more conservative slopes where this problem may exist. These layers are best developed in sheltered terrain on the northern portion of the compass (NW-N-NE-E) at middle and upper elevations.

    Want a little more detail on this? Here is a video from Chris describing the problem in this Zone, and a video from me describing what it looks like where the snow is a bit thinner. 

    ADDITIONAL DISCUSSION An increase in wind speed was recorded in this Zone overnight. There is not a lot of snow available for transport, thanks to the warm storm that brought rain to upper elevations, but there is some. Be on the lookout for small, recently formed slabs if you are traveling in upper elevations in this Zone. Though small, these slabs may be reactive. More importantly, they are adding weight to the weak layers described above.

    (3/2/2022) This series of persistent slabs failed near the tail end of the warm, wet storm last week. These slightly discontinuous crowns span over 1,000' of terrain in this photo, with another 500' of crowns out of frame to the left. The crowns pictured here are on a NE/E-facing slope around 8,400-8,700'. 

Avalanche Discussion

Wow, it has been quite a dry two months in our part of the world! Thanks to a lack of snowfall, we've gone through many weeks of LOW danger across our entire forecast area. These conditions have allowed us to travel freely in the mountains, spending significant time in avalanche terrain in the middle of winter. If you have spent much time around here you know that this is pretty unusual. However, with weak layers buried in the upper portion of our snowpack and snow in the forecast, it is time to begin to shift that mindset.   

The Banner Summit area is a good leading indicator for the types of conditions we may be encountering in the mountains in the coming days and weeks. Here, more snow has fallen and we've reached the tipping point between stability and instability. Numerous slab avalanches occurred here during the storm last week and the possibility of human-triggered avalanches is on the table today. As we travel south, the slab of snow overlying these weak layers is thinner and the likelihood of encountering this problem is significantly lower. Light snowfall returns to the area this evening and continues through Wednesday. Even though we aren't anticipating huge snow totals from this storm, we will be inching towards the breaking point of these weak layers. Take some time today to think about how you are moving through the mountains and how that will change when there is a meatier slab on the surface. In the Banner Summit area, our travel practices have already become more conservative. Further south, it won't take much additional loading before we find ourselves taking a big step back. I hope you have enjoyed the simpler conditions of the past months because our world is set to become quite a bit more complex.

Catch up on what happened with this week's wet, wild, and windy storm in Chris's Weekend Update! 

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