Snow in the PNW 20-21: We may have Corona but Corona doesn't have us!

[Norseman]

Good post about this from a southern neighbor (post 842 in the Oregon thread):

I'm not, I've only spent little bits of time around a few people I'd consider as such, and I want to apologize for any dick measuring intentions or implications in how I phrased my questions in my post.
Because in the big picture - it isn't most important to be able to drop a bunch of acronyms, or whether you consider yourself or others consider you an avalanche expert ...

I've adopted the current mantra of the AIARE Risk Management Framework in saying that what's most important when skiing in the backcountry is recognizing the uncertainty you have about all the variables in front of you, the team, the snow, the stability, weather, terrain, navigation etc, acknowledging what you don't really know, and being able to say if the specific consequences of fucking up are beyond what you can tolerate given that uncertainty. I'm saying this for the benefit of anyone whose ears perked up when they saw my question and your response, because the third part of this post is less important to good decision making than first two bits. Also saying this because the AIARE Recreational curricula have really evolved over the last 5-6 years and for anyone who hasn't refreshed their training in a long while, it's well worth it to just re-take the Rec 1 and Rec 2 courses.


In light of my comment above, props for having a plan, taking observations, and changing the plan to be more conservative when expectations weren't met.
Seems basic but I run into so many people in the backcountry who do none of this ... sigh.



With all that out of the way ...

Yeah my main question was did you have reason to think persistent slab problems were possible, and your answer above is hell yes!

The easy way I see to look at this is that you directly observed propagation potential behavior on a crust that was capped by two other crusts ... something deep enough and old enough (propagation potential persisted through at least two subsequent loading events) that you could call it persistent. Easy. Persistent slab 80 cm big is scary, basically unsurvivable in most types of terrain, large propagation potential, and doesn't heal quickly. Who knows the distribution? Who knows if it will persist beyond this week? With persistent slabs keep the uncertainty high regardless of what weather comes in.

The more complicated way I look at this, I was specifically looking to hear whether you observed any faceted forms like surface hoar or near crust facets, or if you suspected such forms were possible/probable/likely given the weather history in that area. You didn't state anything about grain forms at that 3rd crust, so at risk of presuming nothing was obvious I'll offer an unsolicited tip (apologies in advance if its not welcome), next time you get a shear like that, *especially* if your column fails via sudden collapse rather than sudden planar, lightly scrape your hand and/or a grain card above and below these crusts to see if you can find any obvious or less than obvious angular / cane-sugar / ziggurat like forms. Seeing that would be a major, major red flag to be super cautious about terrain choice.

The key now is to keep that persistent slab on your problem list, and go looking for that interface after this next loading round and set of weather changes to see if you can determine whether the propagation potential is essentially staying the same, getting worse / easier to trigger, or getting more stubborn, or best case you can't really find or identify it anymore, then figure out when you have enough certainty to mess with it on given terrain with given consequences.






Rain can be a double edged sword and we can probably debate over several beers / pitchers / cups of tea for the abstinent about when heavy rain above pass elevations is "needed" or "a good thing." From a stability perspective the big downside to rain, especially early and midseason rain, is what happens *after* it falls ... what happens if it gets really f'ing cold? If the saturated snow and free water on the surface freezes solid you get a thick heavy ice lens that acts as a temperature reservoir and source of water vapor pressure. Then what happens if it only snows a few inches of cold snow on top of that rain crust? What can happen if air temp gets cold and/or clear after that shallow snow falls? The temperature and vapor pressure gradient above (and sometimes below) that rain crust can form near crust facets (NCF) that don't easily heal with subsequent loading and give a veiled indication of strength while actually having shit structure with massive propagation potential. Even in coastal mountains NCFs that create persistent slab problems can actually make for a season long problem that could continue to build up and up into super scary desctructive potential, just ask longtime Baker skiers what they think of raincrust driven NCF interfaces. I believe that later in the season stout rain crusts can also serve as glide layers where free water is unable to percolate below them, so again massive wet slab potential during a melt event of the upper snowpack.

So yes, rain means warming of the snowpack, it means added weight to test any weak layers that might be on the verge of failing, it could mean percolation of free water through various layers. I've even once seen where copious amounts of rain percolated to basal facets formed on the ground and literally froze them into place and turned a persistent slab problem into a melt-freeze snowpack (zero to hero, yay!). But rain is not always *necessary* to resolve a weak interface. Extended periods of near-freezing / warm temperatures are generally what resolves weak interfaces ... and it can do it without washing away precious snow near or below pass elevations.

Granted, so far this season we've been in very warm cycles overall. I haven't been keeping too much attention east of the crest and north of 20, but it just seems like the pattern has been staying warm enough following precip cycles that odds of NCF setup are lower. But like I said, uncertainty.


In my view ... warm spackle snow and a lot of it makes a dense consolidated snowpack that makes a long spring; rain at high elevations melts the snow you were hoping to skin on come Father's Day and 4th of July and instead makes for a longer walk in approach shoes. Although like I did say before, a good mega avalanche cycle followed by reloading of the snowpack can bring dense snow further down into slide runouts that make for possible late season skiing lower down before you're back walking on dirt and rocks (if that slide runout hasn't been suncupped to hell by then).

[kamtron]

Interesting thoughts from you all, it makes for good reading and thinking. There definitely was a bit of clear and cold weather immediately after the New Year's rain event (good boot top pow skiing on 1/2) which I could see forming near crust faceted snow. Then again, we've had a ton of snow on top of that, and fairly moist snow at that, so I'm not sure how much faceted snow survived or not. I haven't dug any deep pits to look at those layers myself, as I've been traveling in such a way that I feel comfortable just evaluating the surface layers of the snowpack.

I like your approach, Gunder, of thinking of low probability & high consequence events especially when given the evidence from the bomb results on the arm. Being newer to the Baker zone, I haven't gone out the arm yet. I was thinking of heading up the White Salmon glacier on Saturday, but decided it would be too risky to be up in that complex terrain with many possible convexities and trigger points so soon after massive snowfall.

I guess no matter what (whether or not we want to call it a PWL or just a possible sliding surface), when we get such large amounts of snow stacking up so fast, it's best to take a conservative approach as the snowpack adjusts to the added load. And luckily, burying such a crust layer deep enough (many meters down) should lead to a favorable situation for rounding over time due to reduced temp gradients.

[steveski]

Good post, schralp knows his shit.

[Gunder]

I guess no matter what (whether or not we want to call it a PWL or just a possible sliding surface), when we get such large amounts of snow stacking up so fast, it's best to take a conservative approach as the snowpack adjusts to the added load. And luckily, burying such a crust layer deep enough (many meters down) should lead to a favorable situation for rounding over time due to reduced temp gradients.

Dont get caught up in the terminology. PWL do not have to just be facets, depth / buried hoar, etc. An ice layer is in fact persistent and it can in fact be a weak layer, so thus it can be a PWL.

Anytime you have a crust / ice layer in a snowpack near crust facets will form regardless of how that crust was buried. Water vapor is always moving up in the snowpack, crusts interfere with that and thus facets will start to form. Facets are also extremely strong in compression and can hold up a ton of weight before they fail. When that actually happens is anyones guess. Ideally we get enough rain to either force that failure along prematurely, or enough water to percolate down and saturate those facets and and then refreeze. Of note some of the biggest sides I've seen at baker involved a crust, where the snow came in correctly on top of it and started off being well bonded. Then it eventually failed months latter after a ton of snow fall. It is also worth noting, that typically in January we have a very stout crust form followed by a cold dry spell (January is usually high and dry here) then lots of snow usually buries it in Feb. So every major slide that has occurred (15+ feet deep) around the ski area has been with in the week before / after March 15th.

The current situation was made worse, sooner by the crust being buried by a layer that didn't stick to it from the beginning, creating a sliding surface that would reload and slide multiple times.

At the end of the day, one of the most dangerous things you can do is to "over think" snow science as anytime you think you can "out smart" a problem you will get spanked. The most important thing for me, when evaluating hazard is constantly asking what's going on thats out of the ordinary? Did we get a big loading event? Was there unusually strong winds? An unusual wind DIRECTION? A unusual dry period? unusual temps? unusual natural slide activity? The list goes on, but anytime anything unusual is on my radar, then I use a lot of extra caution as thats when "unusual" things such a slides, etc will tend to happen.

An unusual wind direction is a big one for me. Anytime a North East system comes in, which usually results in high-pressure we get very cold and very strong winds out. of the NW. That always scrapes snow off of the best ski terrain at Baker and then loads a lot of the terrain that is usually safe even on high avalanche danger days.

[jackattack]

10" of new under light to pissing rain at the windy hill this morning. Steep natural snow was velvety but in classic Mission fashion they sent the cats out in the evening on the only open chair worth riding, so it was 500 vert to 3" of garbage velcro mush on the "groomed" slopes. One and done for me and the missus, not worth a knee injury.

Hoping for percolation and consolidation of the pack.

[volklpowdermaniac]

Dont get caught up in the terminology. PWL do not have to just be facets, depth / buried hoar, etc. An ice layer is in fact persistent and it can in fact be a weak layer, so thus it can be a PWL.

Anytime you have a crust / ice layer in a snowpack near crust facets will form regardless of how that crust was buried. Water vapor is always moving up in the snowpack, crusts interfere with that and thus facets will start to form. Facets are also extremely strong in compression and can hold up a ton of weight before they fail. When that actually happens is anyones guess. Ideally we get enough rain to either force that failure along prematurely, or enough water to percolate down and saturate those facets and and then refreeze. Of note some of the biggest sides I've seen at baker involved a crust, where the snow came in correctly on top of it and started off being well bonded. Then it eventually failed months latter after a ton of snow fall. It is also worth noting, that typically in January we have a very stout crust form followed by a cold dry spell (January is usually high and dry here) then lots of snow usually buries it in Feb. So every major slide that has occurred (15+ feet deep) around the ski area has been with in the week before / after March 15th.

The current situation was made worse, sooner by the crust being buried by a layer that didn't stick to it from the beginning, creating a sliding surface that would reload and slide multiple times.

At the end of the day, one of the most dangerous things you can do is to "over think" snow science as anytime you think you can "out smart" a problem you will get spanked. The most important thing for me, when evaluating hazard is constantly asking what's going on thats out of the ordinary? Did we get a big loading event? Was there unusually strong winds? An unusual wind DIRECTION? A unusual dry period? unusual temps? unusual natural slide activity? The list goes on, but anytime anything unusual is on my radar, then I use a lot of extra caution as thats when "unusual" things such a slides, etc will tend to happen.

An unusual wind direction is a big one for me. Anytime a North East system comes in, which usually results in high-pressure we get very cold and very strong winds out. of the NW. That always scrapes snow off of the best ski terrain at Baker and then loads a lot of the terrain that is usually safe even on high avalanche danger days.

I love your takes, and if I’m reading correctly your general gestalt, I totally agree. I worked in the snow for many years prior to moving in a different direction and had many excellent teachers, but one who stood out was the one who always taught to not get bogged down in the minutia of snow science. Look at the big picture, simple stuff and you can stay alive a very long time. When I was back in my formal AIARE days I always thought that there was too much diving into the snow science, which while great! I feel like is often hard for layman to use effectively and simply. Maybe there is a new approach being used.

[MagnificentUnicorn]

10" of new under light to pissing rain at the windy hill this morning. Steep natural snow was velvety but in classic Mission fashion they sent the cats out in the evening on the only open chair worth riding, so it was 500 vert to 3" of garbage velcro mush on the "groomed" slopes. One and done for me and the missus, not worth a knee injury.

Hoping for percolation and consolidation of the pack.

I can’t believe you put your boots on


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[jackattack]

I can’t believe you put your boots on

gambled and cut our losses.

[wickstad]

gambled and cut our losses.

I stood there for awhile. Went home injury free.

[cascadianwarrior]

I did 3 laps in the trees off 3 (which were pretty decent) but yeah, as soon as you hit the groomers it became glue. Easy call to pull the plug on the day

[Dromond]

Good post about this from a southern neighbor (post 842 in the Oregon thread):

This video I just saw posted on near crust faceting seems relevant to the discussion:

[kamtron]

Thanks for the video! About 10 min in he talks about possible outcomes in a maritime snowpack.

Here's some stoke for you all. First picture from Dec 23, one day after a solid rain event, a good day for facet atop crust surfing.

[Dromond]

...crickets..... well it's at least sunny?

[ridinshockgun]

Surprised there isn't more from Saturday coming in.

[greenmachine]

no shit! keep em coming.

[Skis]

Any idea how the crowds have been with COVID rules at each place? Mostly thinking midweek, but probably end up doing a couple weekend days too. Other thoughts?

[NW_SKIER]

Weekend days? You must like lines.

[AK47bp]

Any idea how the crowds have been with COVID rules at each place? Mostly thinking midweek, but probably end up doing a couple weekend days too. Other thoughts?

Totally!


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[The AD]

Any idea how the crowds have been with COVID rules at each place? Mostly thinking midweek, but probably end up doing a couple weekend days too. Other thoughts?

If you don't like lines head up for night skiing. Obviously that limits the terrain options, but you can lap to your heart's content.

[timeo]

My Crystal experience so far: lines are longer on weekends but not by much. In a normal year, midweek would have zero lines but now they are about 75% of what the weekend lines are so it isn't a huge benefit going midweek. Lines are significantly smaller after around 2PM or so. Also, depends a lot if all lifts are running or not, windhold = huge lines.

Every midweek day I have skied this year the parking lots were filled into F lot.

[Dromond]

My Crystal experience so far: lines are longer on weekends but not by much. In a normal year, midweek would have zero lines but now they are about 75% of what the weekend lines are so it isn't a huge benefit going midweek. Lines are significantly smaller after around 2PM or so. Also, depends a lot if all lifts are running or not, windhold = huge lines.

Every midweek day I have skied this year the parking lots were filled into F lot.

I concur, although maybe on one day I skied the G lot didn’t fill. It’s been busy for sure.

[thejongiest]

I would say COVID-19 restrictions are much tighter at Crystal than Stevens. Crystal has lifties running the lines but at Stevens it was a lot easier to casually pair up. Also, mask enforcement was much stricter at Crystal where they yell at you constantly whereas my experience at Stevens (only one time) is that when you get to the ropes for the lines you should pull your mask up but its more casual and less yelling.

Don't mind either way, but lines seemed to move faster at Stevens.

[timeo]

I will also add that the singles line moves twice as fast as the other lines on Rex based on how they have been loading, they have just been taking a group from each line on Rex which means they take two singles each pass. This is the only chair that works this way because it has one single line vs. two single lines at the other chairs.

[nickwm21]

I will also add that the singles line moves twice as fast as the other lines on Rex based on how they have been loading, they have just been taking a group from each line on Rex which means they take two singles each pass. This is the only chair that works this way because it has one single line vs. two single lines at the other chairs.

As a single you get fucked during the morning rush on Chex. They don’t load a singles chair like they do on Rex.... it will take 2-3 times longer to load than a group of two...


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[phatty]

Posted this in the Alpental thread, but Snoqualmie reposted Thing #2 getting huge at Alpental.

https://www.instagram.com/p/CKEek2sh...d=gssic473fsa6