Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering an avalanche breaking 1-2 feet thick remains possible. Avoiding steep slopes—especially those exposed to the wind—will help you stay out of trouble. While unlikely, we can't rule out triggering a very large, 4-5 foot thick avalanche—especially on very steep, rocky, wind-affected slopes.

Problemi valanghivi

  • Persistent Slabs

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

    The snowpack is deepest in this zone, but the two problematic layers that exist elsewhere are also concerning here:

    1. Surface hoar and facets buried 2' down: The train of storms that brought significant snowfall across our region buried a weak layer that has produced avalanche activity in all of our zones. In the Banner Summit area, most of the activity that we have observed failed on a layer of surface hoar at this interface (photo at right/above). I went looking for this layer in the northern portion of this zone on Sunday (observation here). In places I found surface hoar here and in others I found facets on top of a crust. These layers were stubborn in my snowpack tests, but I still let the presence of these layers drive my terrain selection. Human-triggered slides on these layers are possible again today. You are most likely to trigger one in "prime time" avalanche terrain that has been loaded by the wind.
    2. December facets buried 4-5' down: This layer is deeply buried in this zone but has been slow to gain strength. Because the slab over this weak snow is so thick and dense, it is difficult for us to impact the weak snow underneath, but the bad structure (strong snow over weak snow) isn't improving.  It would take a dose of bad luck to trigger a deep slab, but it could happen in very steep, rocky, wind-affected terrain where more "trigger points" exist.

    We are in the midst of a multi-day wind event that is producing strong W to NW winds. These winds are loading many slopes at middle and upper elevations, keeping these weak layers on edge. Avoiding steep, wind loaded slopes will greatly reduce your chances of triggering a persistent slab avalanche.

    (2/4/2021) This avalanche failed 2' deep on buried surface hoar. This weak layer has presented itself as surface hoar in some areas and small facets in others. NE, 8400', Copper Mtn.

  • Wind Slabs

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

    Because of the weather patterns and terrain characteristics of this zone we don't often see widespread wind slab problems here. I went out to look for wind slab problems in the northern portion of this zone on Sunday. I found plenty of wind and saw lots of snow being transported by the wind, but found that the slabs that were building seemed to be bonding well with the snow underneath. 

    From an avalanche danger perspective, the larger concern is the ongoing loading on the persistent weak layers described above. Even small wind slabs can be great triggers for more deeply buried weak layers. Any avalanche that steps down to these persistent weak layers will be large and destructive.

    ADDITIONAL DISCUSSION: The ongoing wind event is moving plenty of snow, and even though the slabs we've observed in this zone aren't particularly touchy, there has been some significant cornice formation in the past few days. On Sunday, I found large, fresh cornices that were easy to trigger, often toppling off the ridge with a single kick (from a safe distance, of course). As the wind continues, these cornices will be failing naturally, tumbling down the slopes below. These dense blocks can penetrate deeply into the snow as the cartwheel downslope, providing a great trigger for both shallow and deeply buried weak layers.

Avalanche Discussion

I'm going to give you two discussions today, one about wind and snow and one about you and me. There is a lot in here, but I think it is all important. If you've got a few spare minutes pour yourself another cup of coffee and give them both a read.

WIND AND SNOW When we think about the primary factor that is affecting the snowpack are often thinking about storms and snowfall. However, during prolonged wind events (right now), the wind can be a major driver of both avalanche activity and snowpack variability. Over the past 5 days, strong winds have scoured many slopes and created stiff drifts on others. Take a look at this photo I took in the Sawtooths yesterday to get a sense of this. In the upper portion of the image, you can see slopes that have been scoured down to an icy sun crust. In the lower portion, you can see stiff dunes of snow that were deposited by these strong winds.

When the wind blows like it has been, it creates unusual loading patterns. We are used to seeing softer slabs near ridgetops when we think about wind slab problems, but prolonged strong winds can create slabs in places where you wouldn't normally find them (photo here). Hard slabs, like those that have been building, are unpredictable. They are so stiff that they can easily support our weight in many places, making it more difficult for us to impact layers of weak snow underneath. But when we find thinner spots in the slabs, or the edges of the slabs where they taper down, we can trigger slides that propagate long distances, thanks to the stiffness of the slab. 

To add complexity to this picture, remember that this is all taking place on top of a snowpack with multiple proven weak layers. Some of these layers are widespread and some are more isolated. Some have been with us for months and others are new players in the game. Is this all starting to sound complex? I think that is good, the backcountry snowpack is mind-bogglingly complex. Speaking of complex... let's look at what happens when we add humans to the picture. 

YOU AND ME: OUR OWN WORST ENEMIES Since January 30th, 16 people have lost their lives in avalanche accidents in the U.S. This was the deadliest avalanche period in our country in over 100 years. While that is a terrifying, heart-wrenching statistic, the people who lost their lives aren't statistics. They are brothers and sisters, sons and daughters, each with countless loved ones that will never get to see them again. Don't just gloss over this, take a minute to let it sink in.

When we enter avalanche terrain in the backcountry we are playing a dangerous game, one with high stakes and small margins for error. Faced with the harsh realities of the backcountry environment it is easy for us to find ways to explain away these dangers. We do this without even thinking about it, it is a defense mechanism that our brain employs to help us feel comfortable with our choices. We are story-telling animals. We tell ourselves stories that help us to make sense of the world around us. Unfortunately, the stories that we tell ourselves don't always reflect reality.

If you have been backcountry riding or skiing for very long I can guarantee that you have made some bad choices in the mountains. I know that I sure have. If you don't think you have, I suggest you spend some time reflecting on your past experiences. This isn't an indictment of you or me, it is an invitation for us to reflect on our good luck and to learn from it. We learn very little when we think we already know everything. The backcountry environment is a feedback-poor one. Oftentimes when we make bad decisions we don't get any negative feedback from them, just good powder skiing and riding. But that isn't a sustainable way to travel through the mountains. One way to give ourselves more feedback is to do a "debrief" after a day out in the mountains. You don't have to be a snow professional to do this, everyone can benefit from this simple exercise. Here are a few questions you can ask your group to help get the ball rolling:

  • Did we establish a plan in the morning? Did we stick with the plan we established? If not, why did we change the plan?
  • What was the most hazardous portion of the day? Was this a hazard that we anticipated? How did we manage this hazard?
  • Did we find conditions that we anticipated or were things significantly different? Did this cause us to change our initial plans?
  • Did we have any near misses (points at which the day could have gone drastically differently?)

I've spent much of this season worried about my close friends and the people I love who spend lots of time in the backcountry. I've spent much of the season worried about you all as well. I feel incredibly fortunate that we haven't had any serious accidents in our area this season and I hope that the trend continues for us. I know that part of the reason for that is because you have been making good decisions and part of it is because we get lucky sometimes. Waiting out bad persistent weak layers, and sticking to mellow terrain during prolonged instability, requires discipline and patience. Stay the course my friends, there will be times with good stability and steep powder but we aren't there yet. Thanks for reading, and thanks for making good decisions in the mountains. And do me a favor and try a debrief next time you go skiing. Lets keep learning and keep having good days in the mountains

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