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  1. #26
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    Quote Originally Posted by neck beard View Post
    Analyze skier triggered incidents in the last 2 decades in your snowpack and see if you can narrow down the "dozens upon dozens" to at most one dozen weather, terrain and snowpack factors which are common to a significant number of those incidents. I bet you can. That is where rule-based decision making comes from. The trap is that there are times and places where exceptions are required. Those exceptions may merit less or more risk than the rule system indicates is appropriate.
    I suppose you're right. On the other hand, if there are exceptions to the formula then it's not an effective formula by definition. But maybe it has saved lives (?) so that's good.

  2. #27
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    You are right, not really a formula, just a starting point. An awareness tool. An attempt to help build intuition via consistent application of a rule-based form.

    As for saving lives:

    Pick any recent avalanche fatality and see if it would have saved a life

    v.s.

    Pick any highly desirable backcountry ski run that was skied and did not slide and see if that run would have been "ruled out" that day.

    It would have saved the poor snowshoers near Lake Louise (I was nearby that day).

    As for missing out on runs that might slide (but didn't when someone else skied it).... It is a numbers game. Break the laws of nature enough times and you will eventually get an avalanche fine. Kind of like road driving laws. It catches up with you eventually, so I don't speed drunk at night on a wet road with oncoming traffic. ps, I never drink drive anyway.

    Exceptions aside, the bigger shortcoming is that not all valuable data is available to you, particularly at the start of a tour, on a ridge boot pack from resort, in bad vis (due to cloud, forest, terrain). Or bad investigation of the snow as you progress. Or limited public info.
    Last edited by neck beard; 03-20-2017 at 01:16 PM.
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  3. #28
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    Quote Originally Posted by Buster Highmen View Post
    Having done 2 level 1 and 1 level 2 where the level 2 was done at Silverton, a well regarded school in the states, I never heard or read of 'Munter'.

    Admittedly all those classes were quite a while ago, so things may have changed stateside.
    I haven’t taken a formal class in 10 years. If you attend a weeknight talk put on by NWAC they mention the Munter method when assessing risk and travel planning.
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  4. #29
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    I don't think the decision making tools or forecasts were at fault here.

    * The first image shows terrain where stuff can get out of control real quick.
    * The second image shows ski tracks descending into an incredibly obvious terrain trap.

    I used computer modeling to develop some keywords that I use to evaluate terrain. Just use a few of these criteria to evaluate the terrain in those photos.

    Line-Of-Sight
    Is line-of-sight limited? Do local terrain features obstruct your line-of-sight to terrain above or below? Is your uphill view blocked by rocks or trees? Can you see all the terrain below or only some of it? Pay attention and double-check your decisions when line-of-sight is limited for any reason. Limitations to line-of-sight can reduce your reaction time to zero.

    Open
    Is the terrain open enough to produce small, medium, or large avalanches? Are there open breaks in the forest that allow snow to travel unobstructed to your location? How much open terrain is present and where is the open terrain relative to your location? Large quantities of snow can accumulate in open areas near mountain tops before an avalanche and in valley bottoms after an avalanche.

    Confined
    Is the terrain confined relative to the size or speed of an avalanche of any size? Could a large, fast-moving avalanche overrun the valley floor? Are you in a gully where escape from a small but fast-moving avalanche could prove impossible? Small avalanches form deep deposits in confined terrain, such as hollows or depressions, where snow can accumulate. Estimate your reaction time before something goes wrong and double-check your decisions if reaction time is short. Reaction time is a very important part of your margin of safety.

    Accumulation
    Has snow accumulated above or below? Avalanches often start where snow accumulates, and then run downhill where they deposit snow on the valley floor.

    Obstacles
    Are there obstacles above or below? This includes cliffs, crevasses, rocks, and trees. Obstacles above may block your line-of-sight, inducing hazard blindness, and can cause traumatic injuries during any phase of an avalanche. On the other hand, obstacles can block or redirect flowing snow and may offer protection at your current location.

    Steep
    Is the terrain steeper than 30 degrees? Avalanches start and rapidly accelerate on steep terrain. Steep terrain produces fast-moving avalanches that can release above you and travel toward your location. If you trigger an avalanche on steep terrain, you may be unable to escape from the flowing snow. Steep terrain can limit your line-of-sight, and indicate locations suitable for sluffs, cornice drops, serac fall, or rock fall—all of which can start avalanches above or around you.

  5. #30
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    I remember "learning" about munter and 3x3 methods on ttips over a decade ago. For the sake of learning and applicability in NA, these methods were applied by some of the pros and semi-pros on ttips to incidents in NA. my memory of takeaway is that it does not apply to NA. the base of the analysis would need to be revised to address NA statistics.

    Something that i never liked about the munter was how existing tracks reduced the risk (at least that's my memory of learning it).

    wow/wra (one of my instructors, irl, back in "the day") has said something to the effect "unusual weather makes for unusual snowpack." have the areas where these incidents occurred been experiencing unusual weather or unusual snowpack this season, perhaps outside the statistical range where those methods are no longer statistically relevant?

  6. #31
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    Quote Originally Posted by bodywhomper View Post
    wow/wra (one of my instructors, irl, back in "the day") has said something to the effect "unusual weather makes for unusual snowpack." have the areas where these incidents occurred been experiencing unusual weather or unusual snowpack this season, perhaps outside the statistical range where those methods are no longer statistically relevant?
    Yes, something like that. The problems of the current snow situation are not really that much of an outlier compared with the last few seasons, but compared to the typical winter of the 1980s (when I believe Munter came up with his thing) they may well be, I don't know. People are reluctant to question something that has worked very well for the last 20 years and gives very convenient, clear cut answers.

    The wording on existing tracks is "skied a lot all season", which is supposed to mean slopes with actual skier compaction, so really only stuff that is effectively a bump run. This is one of the factors where you can tune the calculation so that you get a green light (there are five tracks here now and i'm sure it was totally skied out before the storm, we can apply another risk reduction factor! yay, now we're below 1!)
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  7. #32
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    Quote Originally Posted by klar View Post
    Which big slide at the start of the season do you mean?
    In the Ferwall Valley in Obergurgl at the end of November. Large group of ski tourers remote triggered the slopes above them. 3 killed I believe.

    I wouldn't necessarily call it at PWL at that point as the snow had only just fallen :-) but it was the start of the PWL. It is more that the weak layer is homogeneous - extending over the whole slope, which is typically of these thin snowpack TG type issues. The Foglietta avalanche in Ste Foy (group with 2 instructors) is in the same class (danger rating 3 - 5 Jan 2015).

    https://youtu.be/1GOgnvOAC7w

    as was the avalanche that caught an army group last season at Valmeinier and the instructor led group at Tignes. I believe the head of piste security at Tignes suggested that climate change may be making certain situations more dangerous - that is, poor snow cover at the start of the season leading to these kind of slides. Someone would need to do some research to see if avalanche incidents are getting more severe (number caught / number killed) over the last years, the trend had been the other way as the message about group spacing had been getting through.

    I see the Swiss guide in the incident above is being prosecuted for manslaughter - the prosecutor said that a North facing steep slope where there had been previous incidents was an unsuitable route choice (I imagine you know more about this being on the ground, I'm just taking what is in the Swiss newspapers).

  8. #33
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    Quote Originally Posted by klar View Post
    The wording on existing tracks is "skied a lot all season", which is supposed to mean slopes with actual skier compaction, so really only stuff that is effectively a bump run. This is one of the factors where you can tune the calculation so that you get a green light (there are five tracks here now and i'm sure it was totally skied out before the storm, we can apply another risk reduction factor! yay, now we're below 1!)
    Yes that's so true. There was an incident a few weeks ago in France where someone said "but it was a tracked slope, we got a RF2 for that" - in fact tracked for them meant a few fresh tracks whereas it practically means "proximity off piste" and perhaps a couple of very popular ski tours in any given sector. Somewhere where any weak layers have been broken up by the passage of skiers since the start of the season.

  9. #34
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    Quote Originally Posted by davidof View Post
    In the Ferwall Valley in Obergurgl at the end of November. Large group of ski tourers remote triggered the slopes above them. 3 killed I believe.
    Ah, yeah, this one. 2 dead, 4 caught, group of 10 from the Netherlands, also with a guide. They had taken a break, dug a pit and decided to continue with larger distances. They then remote triggered the slide. This picture is taken from where the accident report assumes they triggered it.



    There have certainly been a lot of pwl slides all over the Alps this season, as well as the last two winters. I have heard the climate change theory in a few variations. I work in climate science and am a little allergic to blaming climate change for everything, especially using only 3 years as the basis for an argument when you really need 30 to say anything about climate, rather than weather. However, I do see where the argument comes from and the last winters have all been very warm and very dry (dry only in some parts and some months, not consistently all over the Alps).

    There is an interesting article here by SLF employees if you can deal with the german. It points out that in switzerland less people go touring on considerable days than on moderate days but the same amount of people go touring when there is a pwl problem mentioned in the bulletin as when there is not. Using the number of accidents that occurred on days with and without a pwl, they state that moderate days with a pwl are 50% more accident prone than moderate days without a pwl. Considerable days with a pwl are twice as accident prone as considerable days without a pwl problem. They also point out a couple of studies that find that a very large percentage of accidents involving guided groups happen when there is a pwl problem.

    Quote Originally Posted by davidof View Post
    I see the Swiss guide in the incident above is being prosecuted for manslaughter - the prosecutor said that a North facing steep slope where there had been previous incidents was an unsuitable route choice (I imagine you know more about this being on the ground, I'm just taking what is in the Swiss newspapers).
    He is not being prosecuted yet (as in he is not being accused of anything in legal terms. not sure what exactly prosecuted means in english), but they have started an investigation, which they are required to do for any serious incident in the mountains and elsewhere. It is not yet clear whether he will actually be prosecuted for anything, let alone convicted (my guess is that it will go to trial but he will not be sentenced). This news (opening of investigation) has received a lot of media attention because of the still ongoing and still unpleasant conflict between the guides association and the avalanche service. It would really be a lot more noteworthy if they had not opened an investigation.

    The quotes you mention, which are being repeated all over, don't come from the prosecutor but from the head of the avalanche service, which is why the guides are pissed. He stated that it is a north facing, steep slope (an obvious fact). He also said that it was an unsuitable route choice. The bit about "unsuitable route choice" is what is causing the fight. Seeing as four people died this also seems like a fairly factual statement but the guides are saying it is not his place to judge the quality of the route choice at all and definitely not before the official investigation comes to a conclusion. There are many layers of more general issues around all of this. The forecasters (ours and others) are often called upon to act as expert witnesses in such trials, so comments like these by them make the guides nervous. There have also been a lot of fatalities in guided groups the last couple of seasons and people are really starting to wonder and talk. Mountain guides are very highly respected around here and very rarely face criticism, especially public criticism.

    I have not seen any quotes about previous incidents from the forecaster guy. Some of the more annoying news outlets have decided that because of previous incidents the mountain must be some kind of cursed death trap, which no sane person would ever go near.
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  10. #35
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    Quote Originally Posted by klar View Post
    There is an interesting article here by SLF employees if you can deal with the german. It points out that in switzerland less people go touring on considerable days than on moderate days but the same amount of people go touring when there is a pwl problem mentioned in the bulletin as when there is not. Using the number of accidents that occurred on days with and without a pwl, they state that moderate days with a pwl are 50% more accident prone than moderate days without a pwl. Considerable days with a pwl are twice as accident prone as considerable days without a pwl problem. They also point out a couple of studies that find that a very large percentage of accidents involving guided groups happen when there is a pwl problem.
    Thanks for the corrections about the legals.

    That article is really interesting. So why are guided groups getting hit big when there are known PWL problems?

    For "punters" I imagine that many are unaware there is a PWL problem, or even what such a problem is. I would assume guides and instructors would be aware and there would be communication on this. I know in France they have mailing lists where this information is made available. Still if guides didn't go out when there is a degree of danger they wouldn't work much and I guess their job is to navigate around that danger.

    The point you made about the difficulty of guiding and having good group spacing where the risk is of a whole slope going seems to be the crux of the problem. The guide can ski down to the bottom of the slope, beyond the run out, then someone gets into difficulty 400 D+ further up and he needs to help out, well it doesn't really work.

    I suspect enforcing airbags will be the next move for guided groups. I believe Canada is moving down this path. Not sure the slides we've seen are going to be that effective an environment for airbags though.

  11. #36
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    my brief nonprofessional opinion from my desk in california is that to further reduce the risk, the euro risk reduction methods may need to be modified or have another layer of complexity added to account for pwl. this could have a benefit of "punters" reading the warnings more closely and learning about pwl. if that were to happen, i'm curious what the long term results would be....

    one thing that i'm curious about is what guides from the stated or canada think about the use of these methods when they take clients to europe for a trip and hire local guides that use these methods. many of the north america guides are trained avi instructors. if the local guide is giving the green light using a risk reduction method, but the north american guide is seeing red lights, what happens?

    skier compaction: to me, this seems like something that needs to be removed, or lessened in terms of driving the green light decision with the munter method. in unusual winters, shit can hit the fan in unusual ways. i remember taking a course in UT in 2005 or 2006, where pwl, catastrophic/climax slides, and skier compaction were hot topics in the course, because there were big issues with that snowpack. the biggest o shit anomoly(?) was when a steep bump run at snowbird naturalled. it was many days after the last storm, the control work had initially occurred on the run after the previous snowfall, the run had been heavily skied (it was a bump run), and it slide wall to wall at night during a full moon. the bed surface was a bump run.

  12. #37
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    Quote Originally Posted by bodywhomper View Post

    one thing that i'm curious about is what guides from the stated or canada think about the use of these methods when they take clients to europe for a trip and hire local guides that use these methods. many of the north america guides are trained avi instructors. if the local guide is giving the green light using a risk reduction method, but the north american guide is seeing red lights, what happens?
    I was thinking about the opposite as well. Take those euro guides to a typical CO snowpack and see what they think about that...

  13. #38
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    I now feel compelled to point out that the majority of guides here, much like everywhere else, are reasonable and intelligent people, who are entirely capable of having a conversation about risk assessment with people who have a different opinion, and who understand that snow packs are not the same everywhere. As far as I can tell, most guides make decisions through a combination of general assessments (terrain, snowpack, group, etc) and experience based intuition. In practice the Munter calculation is more something they would use to explain/justify their decisions to someone else if asked, or if compelled to do so in a legal setting, not necessarily the foundation of how they made that decision (the latter is probably more true for less experienced people who rely more on a set formula, because they lack experience). As davidof pointed out, for people who get out a lot, doing the actual calculation is something you might use as a confirmation that you're within the limits when guiding a group, to make sure you can justify your decision if you need to.

    The issue with an unusual snowpack is that "experience based intuition" doesn't work anymore. That is not a europe specific problem. If the probability based methods fail, that is just a further symptom of this, since they are also based on previous experiences (accident data). The Euro specific issue is that this may have some yet to be determined consequences if things go to court.

    The german article I linked to cites this older study from Canada, which finds that unexpected avalanches encountered by "experienced avalanche workers" (guides, forecasters, etc) were also largely of the (deep) persistent weak layer variety.
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  14. #39
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    Quote Originally Posted by klar View Post
    The german article I linked to cites this older study from Canada, which finds that unexpected avalanches encountered by "experienced avalanche workers" (guides, forecasters, etc) were also largely of the (deep) persistent weak layer variety.
    I was reading the German (swiss) article you posted in more detail and they seem to highlight problems with interpreting the bulletin when there was old snow situation (no fresh snow for some days) but one which involved a PWL.

    "Für die Benutzer des Lawinenbulletins ist es relativ schwierig zu merken, welche Situation gemeint ist"

    They suggest making the difference clear in the bulletin. We're assuming the user had gone beyond the headline risk which is frequently 2 in this situation.

    The bulletin is also trying to target two kinds of users: backcountry enthusiasts and people concerned with infrastructure, civil defense.

  15. #40
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    Quote Originally Posted by davidof View Post
    The bulletin is also trying to target two kinds of users: backcountry enthusiasts and people concerned with infrastructure, civil defense.
    Yeah that is an old issue that seems to come up every so often. I understand that especially when deciding between 3 and 4 this comes into play and different countries tend to use the danger scale a little differently here. Going by the definitions, 4 means danger to infrastructure (roads). However, forecasts sometimes give a "skier 4", when there is no infrastructure danger but the situation is very critical for skiers. Supposedly this is more often the case in France than in Switzerland or Austria. My guess is there will eventually be two separate scales, but not anytime soon.

    And yes, the problem of people not understanding what the bulletin is trying to say is being discussed here also in the context of the recent accidents. I'm not sure if that is something the forecast needs to work on, or if people need to work on reading more closely. probably a bit of both. Here is another berg und steigen article on that particular subject which I also found really interesting and eloquent.
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  16. #41
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    Quote Originally Posted by klar View Post
    I now feel compelled to point out that the majority of guides here...
    Just to be clear, I wasn't dissing euro guides (if that's how my post came off. I can see how it might have.). I was just pointing out that what may be an unusual snowpack in one place may be the norm in another. Guides do exchanges all the time- perhaps that should be increased as that will spread knowledge of "unusual snowpacks".

  17. #42
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    Quote Originally Posted by klar View Post
    Buster: thanks, that's what I thought. I find the difference in approaches interesting and am wondering why things turned out like this. Here is a kind of general, not very good explanation of what the Munter method is and here is an explanation of how to do the calculation. Here is a practical example. It is surprisingly hard to find english explanations online. Not hard at all in german.
    To make sure I understand http://www.oocities.org/yosemite/tra.../1996/3x3.html <- this resource:

    On a day with what the US would call a "Moderate" deep slab problem (avalanche report 2, danger 4), skiing a 38 degree (RF2) north facing (RF2) slope w/1 partner (RF2) would always be

    Risk 4 / (2*2*2 = 8) = 0.5 = always safe?

    I ask because that is not how I would interpret an avy report that had a moderate risk of persistent slab avalanche on N-facing slopes in eg January here in UT. Bear in mind I am in the US and am also wholly unfamiliar with Munter, just piecing it together from these links you posted. I'm also very conservative in this respect.

  18. #43
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    No, that part is misleading in that link. You are supposed to avoid the Northern aspects, not seek them out. You can apply the reduction factors if you are NOT on Northern sector/half sector slopes. (There are some special rules for wet snow.)
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  19. #44
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    Is there a Bayesian problem with the statistical methods in use? If you're trying to reduce the risk of a specific choice how do you do so without knowing the historical rate? All you know is the absolute historical count of a positive result.

  20. #45
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    Quote Originally Posted by cmor View Post
    Is there a Bayesian problem with the statistical methods in use? If you're trying to reduce the risk of a specific choice how do you do so without knowing the historical rate? All you know is the absolute historical count of a positive result.
    uhhh. I don't think I understand what you mean. Bayesian problem as in a logical cause and effect issue? "Statistical" is perhaps the wrong word for the methods in question, maybe "empirical" would be better?

    If X% of skier triggered avalanches occur in steep slopes with a northerly aspect, avoiding steep slopes with a northerly aspect will decrease your chances of triggering an avalanche to Y%, compared to a chance of Z% (Z>Y) when you select a slope at random from slopes of all aspects and angles. What do you mean by historical rate in this context?

    Should the posterior distribution be reevaluated as more information becomes available (perhaps to incorporate additional "causal" variables), with the result then serving as the basis for a new model? yes.
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  21. #46
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    Quote Originally Posted by klar View Post
    IThe issue with an unusual snowpack is that "experience based intuition" doesn't work anymore. That is not a europe specific problem. If the probability based methods fail, that is just a further symptom of this, since they are also based on previous experiences (accident data). The Euro specific issue is that this may have some yet to be determined consequences if things go to court.
    .
    Experienced based intuition isn't the complete mechanism by any means. I do think is an essential part, particularly when it feels wrong to ski something.
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    Great thread and discussion Klar, thanks for starting it. My $0.25 as a non-professional (CAA level 1 in '96; 1 week advanced refresher in '06) 25 yr back country skier. Nope, don't use the Munter method. Known about it for lots of years as I've done some touring in Europe with a German buddy who uses it as a tool in his decision making process. It was interesting that when touring with Andreas we'd come to the same conclusion (agreement) utilizing different means to come to that conclusion (and through discussion). At the end of the discussion there becomes a "go/no go" decision point whatever method you use (IMHO).

    Agree with Neckbear's comment regarding the avaluator:

    "Keep in mind these are entry-level tools to remind inexperienced people of what should be naturally churning through their head while trip planning, and then all day on the snow."
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  23. #48
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    I really appreciate all the input. This has been interesting, especially in contrast with discussions at home .

    Quote Originally Posted by garyfromterrace View Post
    "Keep in mind these are entry-level tools to remind inexperienced people of what should be naturally churning through their head while trip planning, and then all day on the snow."
    That may have been the developer's intention and how the tools are perceived in North America. However, they are more than that here, hence much of the discussion. In practice, yes, inexperienced people tend to rely on the formalized decision aids to a greater extent than very experienced people. But here the public perception, particularly among people who do not have an intimate understanding of backcountry skiing, is not that these are just entry-level tools. They are considered the standard that separates negligence from bad luck. Notably, the courts tend to agree. That 1 in the Munter calculation has very much become the limit of what is generally considered a socially acceptable level of risk, from armchair QB discussions on the internet, to the media, to legal settings.
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    I find the legal part of this most interesting and something that I was not aware of.

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    Thanks all for the great discussion. I like learning on TGR and this thread delivers.

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