Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Triggering an avalanche breaking 1-2 feet thick remains likely at upper elevations. 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.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    There are two persistent weak layers of concern in our snowpack:

    1. A thin layer of facets and surface hoar buried 2' deep. This layer formed during a week of cold, dry weather, and was quickly loaded by the multiple storms since late-January. Skiers Wednesday on Copper mountain likely remotely triggered an avalanche (photo above/right) on this layer. Observations indicate that it is becoming less problematic, but as persistent weak layers heal, it's not an on/off switch. You could still trigger a slide—it just becomes less likely, and it often takes a prime-time slope angle to trigger one (over 35 degrees).
    2. Our well-known layer of December facets buried 4-5' deep. In contrast to our newer weak layer, this layer formed over a long period (3+ weeks) and was very slowly loaded. Because the slab over this weak snow is so thick and dense, it is difficult for us to impact the weak snow.  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 slopes over 35 degrees and/or those that have been affected by the wind 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

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Welcome to day 3 of our ongoing NW wind event. Yesterday, observers again reported large quantities of snow getting transported. I was above Prairie Creek in the Galena Summit & Eastern Mtns zone and watched the wind rapidly loading a SE-facing slope. Further up the ridge, I remotely triggered a small(ish) wind slab avalanche on this same slope from about 50 feet away. Check out the video (above/right)—it provides an excellent example of how a slope loads, wind slab surface clues, and the end result.

    While the wind event has been less dramatic in the more sheltered Banner Summit zone, sensitive wind slabs remain likely along upper elevation ridgelines. They can be easily identified by surface texture and by their pillowed, rippled, or dune-like appearance. From an avalanche danger perspective, the larger concern is still the additional loading on the persistent weak layers described above. If a wind-loaded slope fails on one of these layers, the resulting avalanche will be much larger.

Avalanche Discussion

This past week has been a terrible one for avalanche accidents in the U.S. Since January 30th, 15 avalanche fatalities have occurred in 8 separate incidents. This has been the deadliest avalanche week since 1910. You can get more details and read the accident reports on Avalanche.org. 

Taking a close look at avalanche accidents is always a double-edged sword. On the one hand, it can provide important lessons on backcountry travel and decision-making. The problem is that we are judgemental—it's literally hard-wired into our psychology to think "I wouldn't ever do that", when in fact it's likely we would. If at any time you feel "judgy" when you read through the reports, I challenge you to think back to when you've found yourself in a similar situation and got away with it. Being empathetic towards the victims, and more critical of ourselves, will help us learn the most from these events. With that in mind, here are a few common threads I've noticed with the recent accidents:

  • Four of the 8 accidents involved multiple people caught. Three of the accidents had 3 or more fatalities. 
  • Several accidents involved skiing or riding in prime-time avalanche terrain during periods of elevated avalanche danger.
  • A few of the incidents involved expert skiers or riders with many years of experience and who were familiar with the area they were in.
  • While many of the reports are preliminary, it appears that the majority of the accidents were the result of persistent weak layers.
  • 14 of the 15 facilities were skiers or hikers.

I am extremely grateful that we've had no accidents this season (knock on wood). I also know that given the long-lasting and uniques instabilities we've experienced this season, that's due in some part to luck. But by and large, we've seen the vast majority of backcountry skiers and riders making appropriate decisions and sticking to conservative terrain. We know as well as anyone that waiting out bad persistent weak layers, and sticking to mellow terrain during prolonged instability, requires discipline and patience. Keep up the good work friends!

Be sure to catch up on what happened last week in Ben's latest installment of our Weekend Update.

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