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

[Norseman]

[waveshello]

That's probably why the westport Sunday surf forecast is calling for 22ft @ 20s.

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[Toadman]

Hurricane headed for the PNW? That looks nice, if it's a cold storm.

[Norseman]

Nah, it'll track north and draw up a long pineapple

[steveski]

is that canyons territory? or looker's left of chair 8 [just OB]?

Yeah I think that's the arm, not Canyon

I thought so too but looking closer on the right it doesn't look like the traverse out the arm. Could be though.

[wickstad]

I thought so too but looking closer on the right it doesn't look like the traverse out the arm. Could be though.

Do they bomb out the arm?

[steveski]

Do they bomb out the arm?

Yes, my understanding is they do targeted control in that area.

However I have not been a baker local since I was a kid so I'm not a good source of knowledge.

[wickstad]

Yes, my understanding is they do targeted control in that area.

However I have not been a baker local since I was a kid so I'm not a good source of knowledge.

there is a huge crown up above chair four.

[ASP]

According to the NWAC post it was on the arm: https://nwac.us/avalanche-forecast/#/west-slopes-north

[AK47bp]

Beautiful day today. Stuck with the kid at West, nice chalky grippy groomers though.



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[Patarero]

Today was mediocre....north facing goodness.

[wickstad]

According to the NWAC post it was on the arm: https://nwac.us/avalanche-forecast/#/west-slopes-north

Still would be same conditions above the canyon.

[f=ma]

Do they bomb out the arm?

Yes, my understanding is they do targeted control in that area.

However I have not been a baker local since I was a kid so I'm not a good source of knowledge.

Yes, they bomb the arm and out of bounds area. In fact I took a video of the helicopter this morning.

[Gunder]

For clarification, they only bomb the arm when there is significant potential for a slide to come in bounds. Hemispheres does get "controlled" with the avalauncher every control day, but thats pretty much just a pea shooter... So Its still basically best to treat it as uncontrolled terrain. The slide on the beast "first knob on arm" in the pic referenced earlier was also from an avalauncher and that is a quite small charg to trigger such a deep layer.

They typically use 50lb bags for the Heli bombing, but it was most likely too cold when they did it for it to be effective. I've seen them do it a handful of times over the last 20+ years. Sometimes it is quite effective, other times no results and a weather event ends up bringing it all down anyways. I am willing to bet if it was 5+ degrees warmer at the time it would have been more effective. It will be interesting to see what this weeks pineapple express brings down. I did a few pits yesterday and while there is no way a skier could trigger that layer, a temp spike and or heavy loading most likely would. There is also a layer thats a bit more reactive around a meter down, that if triggered could potentially trigger the much deeper PWL.

Of note there was a very large slide that occurred some time towards the end of the last storm cycle where the entire slope above the artist point road pulled out ~3 feet deep and ran over the road and took out the lower slope as well. Thats not exactly the steepest terrain and doesn't slide very often and certainly not that deep or wide. It also ran on a slope that had previously slid, so it reloaded and still went on the same layer.... very strange for this area.

[wickstad]

For clarification, they only bomb the arm when there is significant potential for a slide to come in bounds. Hemispheres does get "controlled" with the avalauncher every control day, but thats pretty much just a pea shooter... So Its still basically best to treat it as uncontrolled terrain. The slide on the beast "first knob on arm" in the pic referenced earlier was also from an avalauncher and that is a quite small charger to trigger such a deep layer.

They typically use 50lb bags for the Heli bombing, but it was most likely too cold when they did it for it to be effective. I've seen them do it a handful of times over the last 20+ years. Sometimes it is quite effective, other times no results and weather event ends up bringing it all down anyways. I am willing to bet if it was 5+ degrees warmer at the time it would have been more effective. It will be interesting to see what this weeks pineapple express brings down. I did a few pits yesterday and while there is no way a skier could trigger that layer, a temp spike and or heavy loading most likely would. There is also a layer thats a bit more reactive around a meter down, that if triggered could potentially trigger the much deeper PWL.

Of note there was a very large slide that occurred some time towards the end of the last storm cycle where the entire slope above the artist point road pulled out ~3 feet deep and ran over the road and took out the lower slope as well. Thats not exactly the steepest terrain and doesn't slide very often and certainly not that deep or wide. It also ran on a slope that had previously slid, so it reloaded and still went on the same layer.... very strange for this area.

Has it ever slid up into the ski area that you know of?

[Gunder]

Has it ever slid up into the ski area that you know of?

Yes, the night of March 17, 2012 It went so big, it took out all of the old growth trees at the return to ski area from the arm. There was debris all the way to the base of 8. That area is now known as Herb's berm as Herb built a massive earth berm there the following summer to help protect the base of chair 8. See attached images. FYI the one of the fracture is from when we finally got the vis to see it after another several feet of snow had fallen on it. The last pic is looking at the area of rumble gulley where you normally return to the ski area. Thats normally a deep ravine.



I damn near died that day, as we where skiing some very thick old growth trees in another area, heard a slide come down, and by the time we got to the creek drainage for our exit, a massive slide had come down off of the backside of Mt. Herman / Stoneman area and punched out 200+ feet of old growth and buried the creek bed 40+ feet deep and that was damn close to a mile away from the slope. I've seen some damn big slides, but never fathomed anything going that big and traveling that far into the flats. It significantly widened that slide path by serval hundred feet too.

[kamtron]

There is also a layer thats a bit more reactive around a meter down, that if triggered could potentially trigger the much deeper PWL.

Do we really have a PWL at the moment? NWAC hasn't been talking about anything like a PWL in the NW part of the state. I'd characterize our snowpack as generally well-bonded with a couple interfaces (pretty far down) from rain-on-snow events 1/1 and sometime mid December. It seems like there's the possibility of getting a slide on these deep layers with monstruous loading like we've had (especially significant rain-on-snow, like is happening today/tomorrow, or maybe come spring when water percolates down). I'm just not sure I'd characterize it as a PWL, as I haven't heard of facets or other persistent snow forms at the interface.

That slide on the arm was deep but it'd been snowing like mad + S winds, NWAC characterized that slab as a windslab and that makes sense to me.

[Gunder]

Do we really have a PWL at the moment? NWAC hasn't been talking about anything like a PWL in the NW part of the state.

That slide on the arm was deep but it'd been snowing like mad + S winds, NWAC characterized that slab as a windslab and that makes sense to me.

I have been able to get results on that ice layer as well as a layer above it in every pit I have dug since it initially formed (including on SW slopes that face directly into the wind). I have also seen several slopes slide, reload and slide again on that same layer. From past experiences in dealing with such a deep layer, I like to treat it as a classic low probability high consequence scenario. There was enough weird activity and in areas that are unusual, for me and the crews I ski / work with to treat it as such. Clearly the ski area thought the same and invested the funds in a Heli bombing operation as well. You won't find me near any big terrain until we get a solid rain to the top event. (hopefully tonight). NWAC is a great resource, but as with every avalanche forecast its only one tool in the bag and I always put more weight on first hand experience and what I find in the pits I dig and the activity that I have seen in the area.

Thats just my option on the situation, you may have higher confidence than me in the current snow pack. I have just seen enough massive slides around Baker over the years in similar situations, to give the current snow pack a fair amount of respect and caution.

[powder_to_the_people]

You won't find me near any big terrain until we get a solid rain to the top event. (hopefully tonight).

Sounds like this has an obvious answer, but why would rain on the snowpack get rid of the PWL?

Only scenario I could think of is if the rain water percolates all the way down to the PWL and then freezes when the temps drop again; but would that happen if the PWL is buried a few feet down in the snowpack?

[volklpowdermaniac]

Sounds like this has an obvious answer, but why would rain on the snowpack get rid of the PWL?

Only scenario I could think of is if the rain water percolates all the way down to the PWL and then freezes when the temps drop again; but would that happen if the PWL is buried a few feet down in the snowpack?

You’re onto it. Early on rain creates a new immediate danger with a heavy load, as it filters down throughout the pack, it creates a more homogenous snowpack reducing weak layers, and improving overall strength. This takes a little time though.

[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.