Avalanche Discussion

It doesn't really matter if this year's snowpack is set up worse than last year's snowpack because no one here, myself included, is going to stop skiing. Therefore, the first line of defense is guarding against perceptual errors because such errors are always more dangerous than the state of the snowpack. Sorry to get metaphysical but the snowpack just "is". I mention this because there have been some pretty insane posts in the Trip Reports with respect to perception of instability ( along with some interesting errors and misconceptions being passed around in this thread. ) Perception of instability has not been mentioned once in this discussion so far. NWAC produces incredible forecasts but those forecasts are simply not applicable at the slope scale.

Can you explain this more?  I'm not sure what you're getting at...

It absolutely matters if the snowpack is set up badly and will 100% effect my decisions when I go skiing.  Stop skiing?  Certainly not, but it's not a binary choice.  If the snowpack is fragile, I'll hunt out trees and low angle slopes and approach anything steep with more respect and caution than I would if we had a predictable, bombproof base.  How does the pack's instability not matter?  And we're skiing the slopes that NWAC is discussing in their forecasts... slope scale?  

Maybe I'm not understanding what you're getting at.  Can you elaborate?

EDIT -- looks like you explained it some -- I see where you're going with it now. Though I know I make go-no go decisions from time to time based on the forecasts. Usually it's not "no go skiing", but it influences the destination without a doubt.

Just a few additions to BirdDog's post and a few other posts here. In 2003 the problem was layers that *weren't* deeply buried. ( BirdDog, maybe you meant "very deeply buried" relative to the total height of snow? ) The snowpack was much thinner than usual in 2003. As most people here know, the large fatality count in 2003 ( in BC ) resulted from two incidents in which a large number of people were simultaneously placed in harm's way. Either of these events could have happened in any year ( with any snowpack ) as recent events have shown.

It doesn't really matter if this year's snowpack is set up worse than last year's snowpack because no one here, myself included, is going to stop skiing. Therefore, the first line of defense is guarding against perceptual errors because such errors are always more dangerous than the state of the snowpack. Sorry to get metaphysical but the snowpack just "is". I mention this because there have been some pretty insane posts in the Trip Reports with respect to perception of instability ( along with some interesting errors and misconceptions being passed around in this thread. ) Perception of instability has not been mentioned once in this discussion so far. NWAC produces incredible forecasts but those forecasts are simply not applicable at the slope scale.

You are correct, the large number of fatalities was in part due to the fact that a large number of people were placed in harms way. Another factor was the size of the releases. You write about the perception of instability. In the 02/03 Kooteney snowpack, a weak layer formed in late November. This weak layer persisted throughout the season, until it caused releases, some as late as March. The perception of instability (in late season) was in part masked by the fact that the weak layer was deeply buried; meaning the weak layer was at the bottom of the snowpack; and thus often overlooked, especially when digging pits which generally are not dug to near ground level (at least not while skiing).

You are also correct in stating avi forecast are to be applied in a general sense and are not to be taken as gospel for any one slope at any given time. My concern this year is the current weak layer will become deeply buried as we receive more snow and may persist for some time, possibly into spring. NWAC has stated this.

So, how do we judge the perception of stability/instability later in the season with a weak layer near the bottom of the snowpack? How do we adjust our decision making to account for this?

We'll certainly be skiing, but we may not get onto the steeps at all...

Then how will you create the momentum necessary to go down the hill and make turns?

Then how will you create the momentum necessary to go down the hill and make turns?

Seriously? :

I don't have any answers on how to account for perceptual errors ( i.e. the persistent forms are associated with higher levels of perceptual errors because they're out of sight and often out of mind and harder to trigger when buried deeply, etc. ). Perception of instability is much better for new snow because the instabilities are often near the surface. Some of my thoughts on this snowpack discussion are: we're getting some older information ( now the prior ) and some newer information ( the current ) and I'm not really sure how to sort out what is hard snowpack data and what is speculation. No problem with speculation or forecasts in this thread but I don't really know how to make sense of the information. Second, the data in this thread doesn't really refer to the spatial scale of weak layers noted by observers, which makes it difficult for me to understand where the weak layer might be a concern. Over a wide area? A small area? A single drainage?

I guess my approach, for my own tours, is really trying to be extremely objective about the snow over which I'm traveling, rather than thinking about what the bulletin said. I may choose one area over another ( or I might stay home as I did this weekend ) based on the bulletin but I don't choose aspect or specific slopes based on the bulletin. Also don't tend to pay attention to the instability rating in the bulletin because it can be much higher or much lower than wherever I'm skiing.

When I say that the snowpack doesn't matter, I am referring to my earlier comment: "the snowpack just is". Everyone, including myself, is going to ski this snowpack, so the state of the snowpack is simply something to accept. So I guess this is my way of saying that I've accepted the instability and prefer to plan around it rather than trying to outsmart it or whatever. For example, orographic snow can be a highly localized phenomenon. Therefore the NWAC bulletin might forecast "moderate" danger or even "considerable". However a small ridge might receive much more snow ( 10x ) than the surrounding terrain. In that case, danger at that area could very well be extreme, even though the forecast said "moderate".

To address an earlier question: Avalanche forecasting has several scales. Synoptic, meso, micro ( and possibly slope depending on your training and interpretation. ) NWAC bulletins apply to the synoptic scale and meso scale but do not include evaluation of instability for specific slopes. Similarly, avalanche forecasting has two primary scales: space and time. Forecasting difficulty ( and error rate ) increase as spatial size increases and as length of time increase. It's much more accurate to forecast instability for a single slope for a very short length of time than to forecast instability for an entire mountain range for three or four days. In any case, the NWAC bulletin includes information about aspects and elevation bands that can be used as part of a slope scale forecast but this information should *never* be used alone.

I suppose my real question is as follows: since data sampling forms much of the basis for perception of instability, if we are supplying observations and discussion here, how are we going to supply the information so that it's most useful? Just knowing that weak layers exist ( or that the snowpack is upside down ) doesn't really help much. Furthermore, I'm not entirely convinced that ( set up poorly or not ) the snowpack is primarily unsafe. According to The Avalanche Handbook, the seasonal snowpack is stable most of the time; the snowpack is seriously unstable for only a few hours each winter.

It's the prevailing state ( conditional instability ) that concerns me. This is where the snowpack is mostly stable, except maybe triggering level is a little lower than usual, and maybe pockets of instability aren't quite as rare as one would like. This problem doesn't require widespread instability across an entire mountain range ( which the "poor set up of the snowpack" portion of this thread seems to discuss. ). Conditional instability just requires a patchwork of time-dependent critical flaws with (n) areal size and (m) distribution ( both at random ) to create a nice mess for everyone. Personally, I think it would be fantastic if instability were found everywhere across the Cascades because then a nice big cycle could clean things out. It's secretive instability that worries me. ( Perception wise ).

Second, the data in this thread doesn't really refer to the spatial scale of weak layers noted by observers, which makes it difficult for me to understand where the weak layer might be a concern. Over a wide area? A small area? A single drainage?

Every pit I've dug this new season I've seen one commonality - a persistent faceted crust at or right near the ground.  This goes back to early snows in November as well, and on just about every aspect you can imagine.  From North Cascades to South.  Everything above this layer has been varied and hasn't carried over as "true" from one aspect to another, or from one area to another.  We've found safer areas to ski using data we get from the layers above this faceted crust.

To address an earlier question: Avalanche forecasting has several scales. Synoptic, meso, micro ( and possibly slope depending on your training and interpretation. ) NWAC bulletins apply to the synoptic scale and meso scale but do not include evaluation of instability for specific slopes. Similarly, avalanche forecasting has two primary scales: space and time. Forecasting difficulty ( and error rate ) increase as spatial size increases and as length of time increase. It's much more accurate to forecast instability for a single slope for a very short length of time than to forecast instability for an entire mountain range for three or four days. In any case, the NWAC bulletin includes information about aspects and elevation bands that can be used as part of a slope scale forecast but this information should *never* be used alone.

I suppose my real question is as follows: since data sampling forms much of the basis for perception of instability, if we are supplying observations and discussion here, how are we going to supply the information so that it's most useful? Just knowing that weak layers exist ( or that the snowpack is upside down ) doesn't really help much. Furthermore, I'm not entirely convinced that ( set up poorly or not ) the snowpack is primarily unsafe. According to The Avalanche Handbook, the seasonal snowpack is stable most of the time; the snowpack is seriously unstable for only a few hours each winter.

Agreed that this information should not be used alone.  That's why regular bc travelers' pit info and observations can be so important to friends who travel the bc, TAY, or NWAC - because we take into account the micro scale as you say.  Pits, rouchblocks, ski cuts, turning around - it all helps to evaluate conditions, and sometimes can be pertinent enough for NWAC to put up a specific orographic warning.  Hence, bc travelers in communication with each other and organizations like NWAC and TAY are able to share this info with one another.  Knowing weak layers are present IS important and does help.  I think it helps us to analyze possible scenarios that could occur in present conditions, that might not be considered if the snowpack was laid out differently.  As far as the avalanche guidebook's comment on snowpack stability, I would say that fits into the "information that should never be used alone."  The first weekend in December last year proved that wrong as the snowpack was incredibly unstable for almost 2 days straight.  NWAC posted increasing danger from high to extreme, and even in the areas we thought were relatively safe, we had telltale signs of instability.  Enough to make me turn around and wait a a few days to go back out.

_{Edited for grammer.}