I'm not a citizen, I just live here. Maybe that's why I can't decide if I like the test or not.Quote:
Originally Posted by Summit
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I'm not a citizen, I just live here. Maybe that's why I can't decide if I like the test or not.Quote:
Originally Posted by Summit
The incredibly knowledgable person who is responsible for our local avalanche forecast has explained it to me like this: The PST is nice as a demonstration if you want to show people a block of releasing snow. The ECT will show you weak layers and give you and idea of what they may do, the PST will give you an idea what the layer may do but you have to know exactly where the layer is beforehand. From a purely "huh that's interesting" point of view the PST is very cool and apparently some significant success has been achieved regarding understanding the mechanics of fracture propagation with the help of systematic PST experiments and high speed cameras. From a "do I want to ski this" point of view I have yet to hear an argument how the PST could be superior to the ECT.Quote:
Originally Posted by Z
I also enjoy the podcast a lot. However, I just tried to listen while also following along with an online yoga video and I fell over attempting firefly pose, so I'm blaming covert for that.
The ECT only produces reliable results on weak layers buried less than about 100-130cm below the surface. The PST is effective on weak layers at deeper depths. To me, that seems like the main advantage. If I'm curious about a layer in the upper 100cm-ish of the snowpack (which is most of the time) I'm definitely going to default to an ECT. About the only time I'd do a PST is when the layer is deeper than that, or a layer won't propagate in ECTs and I want more data.Quote:
Originally Posted by klar
Not that pit results should really be answering "do I want to ski this" to begin with, of course.
Yeah fair point. Anything deeper than a meter or so hasn't been very relevant with the crap winters we've been having... I have heard of people doing deep tap tests for this but never seen one done/tried myself.Quote:
Originally Posted by adrenalated
yes poor phrasing on my part. I guess I was trying to say that I find the PST gives more abstract information. What exactly is the data you gain from doing a PST when you want more information? Can you give an example where you learned something from a PST that you didn't know before?Quote:
Originally Posted by adrenalated
the only quantifiable value is the cut length, no? On an intuitive level I find it a lot more difficult to relate that to skiing than how hard/often I hit an ECT block.
Also the fracture character, ie does the fracture shoot to the end of the column, stop before reaching the end, or shoot up through the slab? See page two here: http://www.alaskasnow.org/wp-content...p-Saw-Test.pdfQuote:
Originally Posted by klar
Definitely worth noting that PST shows more false-stable results than other tests.
So as a hypothetical, let's say I want to investigate a layer of facets buried 110cm deep. I do an ECT an get moderate results, but no propagation, something like ECTN14. I might consider doing a PST to see if I can get a fracture to propagate that way. If I get PST-SF or PST-arr it would give me greater confidence in the ECTN result.
All that said I learned the PST two years ago and I think I've actually used it only once since then.
Okay, makes sense.Quote:
Originally Posted by adrenalated
Similar time line for me. I can see the value of added information in specific situations as you detailed but it doesn't seem practical as a go to everyday thing.Quote:
Originally Posted by adrenalated
Side note re fracture character: This year our avalanche center redid the little booklets they hand out to write down pit data and test results so that the only differentiation for fracture character in the ECT is N or P, while previously there were several options in between. The argument was that the in between options only confuse the observers and don't help the forecasters enough that dealing with potentially inconsistent info is worth it. There obviously is value in the more nuanced data on fracture character but apparently when collecting data from an observer network for operational forecasting it is preferable to keep things as simple as possible. I found that interesting.
SWAG was changed to discourage the rating of fx character for ECTs. The reason is that fx character ratings were developed to give an idea of propagation potential. The ECT was developed for the same reason, and the developers feel that adding a fx character rating to it is redundant.
This was pretty legible; consider removing more vowels.Quote:
Originally Posted by covert
I feel like a lot of Avy 1 students come out of the class all gung-ho to dig pits wherever they go, when it seems like in most circumstances, as adrenalated mentioned, pit tests usually aren't there to answer the question of "should I ski this or not." I'd be interested in hearing more about matching avy forecasts to big-picture terrain choices, particularly if you don't have a long history with a particular zone. As well as how those plans might be altered by localized observations.
The deep/hard-slab thought process is generally the response I get when asking professionals about the PST. I suppose it could also be useful for a shallow soft slab where your ECT just compressively (did i just make up a word?) breaks through the slab. Realistically you'd probably feel this underfoot and not necessarily need to dig, but I've been surprised before. Could also help to identify a storm snow interface like preserved stellars or just a tough to detect storm intensity change.
I think I'm looking for some sort of reason to use the test in a real world situation, and I'm not necessarily finding it....As a forecasting tool - maybe, from a daily guiding perspective - not so much?
The avi center covering the Tahoe area has been using pst on some of the early season deeper layer problems that we've had the past few seasons. It's been used to check on changes in the bonding strength of known problem layer(s). They've focused on distance of the saw before failure. Results have influenced their public forecast and their prediction when there's a bunch of water heading into the area.
The "critical cut length" is being used as a kind of proxy for stability and is a main variable in a new-ish theoretical approach to crack propagation by Gaume et al (2015) combining some aspects of Heierli's anticrack idea and more traditional approaches. Unlike the anticrack theory, the new idea shows a dependency between slope angle and propagation (i.e. critical cut length). Apparently PST results can be modeled very well using a FEM.Quote:
Originally Posted by bodywhomper
Not terribly useful for skiing but my inner nerd enjoys this and I bet anyone who has tried to get a finite element model to do something would be appreciative.
https://www.youtube.com/watch?v=Tqok...ature=youtu.be
listened to most of these on our journey to and along the bc powder hwy
long time ago mr tremper autographed his book for me somethin to the effect of sharing a journey of becoming avalaunche experts
somewhere along that journey lots of learnins some formal ,most in ,mistakes, lost friends and a bunch of good shit too
i realized i just wanted to be an addict with a strong dose of self preservation and a solid partner
thanks for producing strong content that fits my goals
its damn good
muchas gracias, sorry i've been slack on keeping up with it lately. i'm returning to the san juans next week and should have the time to finish the season strong.
Fill your quota of turns and podcast as time allows...we get paid by the hour out here
Doug-san,
May we anticipate a new episode soon?
Arigatou gozaimasu
Do itashimashite. You may.
It's back.
Special snacks for anybody that can identify at least three of the technical details I should have explained differently.
Stoke.
In case anyone isn't aware: easy to support this every month with a small subscription via Patreon: https://www.patreon.com/avalanchepodcast
It’s great to hear another episode. I think the recurring cadence is a good way to rehash and reinforce information.
Thanks. I used to be wary of repeating myself, then I realized it's often necessary to beat the shit out of that mule.
Quote:
Originally Posted by covert
1) Your probably not happy with spatial distribution, isolated vs. specific. et all.
You can have specific, widespread problems (that may be easy to avoid, stay off the sunny slopes)
Non-specific, isolated problems sound scarier (the wind destroyed most of the surface hoar, also the wind shifted from the south to the north as the storm rolled in, so good luck finding it)
But then you say likelihood is a function spatial distribution, but you never give us the function.
2 ) estimation vs. probability vs. qualitative vs. quantitative . A model estimate is an estimate of the probability that an event will occur, based on a probability model.
I think your trying to say if you don't put a unit of measure next to your estimate, it doesn't become a measurement ,. i.e. you deliberately introduce ambiguity into your estimate to drive home the fact it's an estimate vs. a hard number made with a limited data set by using your own made up units to drive home the fact it's an estimate vs. a hard number made with a limited data set.
Bossman: Sfotex, how long is it going to take to do the XYZ project?
Me: Considerable time
Bossman: Considerable time? what does that mean.
Me: Well, I estimated the ABC project to take moderate time, and considerable is greater then moderate. If I give you estimates in days your going to hang your hat on it and make plans off of it..
Then you kind of interchange Estimative Probability and qualitative but never bring out quantitative. When you go build your McMansion in Ophir at the bottom of slide path some home insurance company is going to looking at quantitative numbers when they come up with your insurance rate.
Yo thanks for playing,
I think describing a problem as specific and widespread or non-specific and isolated is not consistent with the model. The sunny slopes example that you use would be consistent with a distribution of "specific" where "The problem exists in terrain features with common characteristics." I think your surface hoar example fits precisely with the definition of isolated. I see what you're saying, but would describe those problems differently.
I believe I say Likelihood is a function of Spatial Distribution and Sensitivity to Triggers, maybe that wording could have been more clear, but I do reference the matrix for deriving Likelihood from Distribution and Sensitivity. It gets to be kind of a word salad in the segment. Hard to get around that.
On the other hand, yup, not happy with the discussion of estimative probability; brevity would have been better there. I could have focused more clearly on how those words convey estimates and uncertainty, but I left out quantitative measures on purpose.
During the Story Time I reference an ECT test where I rate the fracture character. In the new SWAG, rating fracture character was specifically removed from the ECT process...because the ECT itself is designed to assess fracture.
I think there are one or two more bits I would have changed, but I forget what they are.
Thanks for the feedback. It's really helpful to hear how folk are pickin' up what I'm layin' down. It also gives me the opportunity to add clarity in subsequent episodes.
But specific doesn't imply distribution, it just says we know the problem exists, i.e. we know there is deep slab instability. Distribution could tell me where (north facing slopes) , and isolated widespread would describe the probability it is there in a given location or area.Quote:
Originally Posted by covert
(you asked for 3, so I was digging hard...)
3) Evidence and uncertainty, you say that uncertainty may undermine evidence, and there is a evidence uncertainty balance. Uncertainty would describe the gaps in our evidence. Lots of evidence may reduce uncertainty, but uncertainty may also linger. So maybe evidence -uncertainty gap would be more accurate? So I may dig a pit on a slope and gather some evidence and my uncertainty will, based on my random sampling of the slope and what I'm looking for, may stay the same. Or it may go down (yup, there's the buried surface hoar I'm worried about)
Looked up Sherman Kent's paper, thanks for brining that up, it's interesting stuff. Nothing like curling up with Words of Estimative Probability on a Saturday night.
"Specific" is a Spatial Distribution rating in between Isolated and Widespread. It has defined parameters for spatial density and available evidence. "Isolated widespread" is a combination of two distribution ratings at opposite ends of the spectrum.Quote:
Originally Posted by sfotex
Attachment 216685
Typically a distribution rating is coupled with additional location information that references aspect and elevation or vegetation band. For instance, Deep Slab problems are possible in specific areas above 11,000 cubits on N-NE aspects.
Some folk like to speak of knowledge gaps, but I prefer balance. Uncertainty may reference gaps in evidence, but it can also refer to the quality of evidence, the unknowable, and shit we could in theory know but don't even realize we need to know that shit. :confused:CrapQuote:
Originally Posted by sfotex
Interesting, your linky is broken but I found this with Google:Quote:
Originally Posted by covert
The Conceptual Model of Avalanche Hazard
(Statham et al, 2010) defines three levels of spatial
distribution: isolated, specific and widespread.
Matched with avalanche size, this information is a
general overview of where, and how big the
avalanches might be.
So the UAC uses these terms (or has in the past)
The Spatial Distribution (isolated, localized, widespread) to include our danger rose aspect/elevation diagram.
https://utahavalanchecenter.org/blog...danger-ratings
I guess thats why I was really really confused.....
Well, since I fucked that one up, I'll have to submit another answer. (Monty Python style): You weren't specific enough on which cubit measurement unit you were using, a cubit can be 17.5 inches or 18 inches. Well, it can actually be a range between 17-20 inches. Context matters. ;)
This is a lot of work for a special snack.
It's getting much better down here, but you'll have to go to Canada for true consistency.
Just listened to S1E10. Two questions:
1. After you dropped in first and found unexpected windslab, where would you have told Zeppo to ski to avoid your route?
2. Would it have been faster or easier to have your skis pointing the opposite direction to avoid the kick turn when you bailed from your post-up spot?
Thanks.
I'm guessing at the story you are referring to, but I think I know the one.
1. I would have told him to avoid the start zone entirely and skirt the path through the trees skiers right.
2. Yes, but I flip lightning kick turns in my sleep. Pisses the wife off. On a more serious note. That would have been a concern for me if I was standing on a slab, where available reaction time would be marginal to non-existent. If you feel threatened by the snow under your feet, it's a good idea to point your skis in a safer direction...and maybe even go there.
Thanks for the response. Any way to make a one-time donation?Quote:
Originally Posted by covert
Yup, go to www.avalanchepodcast.com and click on the Donate via Paypal button. Cheers...dk
Hey man,
Just found your podcast and heard mention of this thread too. Working my way through the episodes but just wanted to let you know Im digging it and appreciate the content.
How about more on snow science, weather patterns and the layers they create.
Right on, gracias, copy that. I should probably do some more ax character type review which would include their formation parameters...
Just wanted to chime in on how much I get from this podcast. After discussing a line with my partner for 10 minutes then realizing we were talking about different things I remembered that very story from the pod!
Nice, I told a story yesterday in class about spending ten minutes talking with a buddy about a piece of terrain before we realized we were looking at different pieces of terrain.Quote:
Originally Posted by chiller
Listened to the last couple episodes on the walk to work today. Enjoyed the Airbus plug.
I stumbled on the podcast a couple months ago and was blown away by how great they are. I've been recommending them to everyone I ski with. I'll probably re-listen to them again before next ski season...
Just found this podcast -- excited to listen to more!
Had this podcast suggested to be my mag SchralphMacchio a few weeks ago and am stoked to have started listening to it! Through ep. 9 of the first season and driving up to Bozeman tomorrow so will be listening to a few more. Thanks for doing this, really appreciate the insight, discussion, humor, and stoke.
Really great stuff, can't wait for next season. Thanks!