DPS Problem in Tahoe, spring 2018

[SchralphMacchio]

Remote triggers with 4-8’ crown depths, failing on NCF.

It’s not a common thing to see in Tahoe. This one might not be going away any time soon, unlike other PS problems in Tahoe that round out, fail and flush during storms, or get soaked in rain.


March 3 - remote trigger from skin approach
https://www.sierraavalanchecenter.or...er-ridge-slide

March 4 - remote trigger from digging pit
https://www.sierraavalanchecenter.or...e-negro-canyon

[TahoeJ]

Based on the last few seasons, I'd say it's starting to become common in Tahoe. Unfortunately.

Not looking forward to high consequence moderate days... it's just like Colorado.

[SchralphMacchio]

March 3, Natural on Trimmer
https://www.facebook.com/groups/1150...8735182810035/

March 4, snowmobile trigger out of Blue Lakes Area
https://www.sierraavalanchecenter.or...akeslost-lakes

[hutash]

I assume Tahoe is like Mammoth this year, a bit of an unusual snow pack. More intermountain then maritime, and all the associated avi issues. Play safe out there.

[Core Shot]

Remote triggers with 4-8’ crown depths, failing on NCF.

March 4 - remote trigger from digging pit
https://www.sierraavalanchecenter.or...e-negro-canyon

Wowee
That must have been interesting

This avalanche was triggered while digging a snowpit to test the buried facet layer. This site was selected due to its similar aspect and elevation to where the Schallenberger Ridge avalanche had occurred the day before.

Once the snowpit depth reached 10 cm (4 inches) above the weak layer (about 140 cm or 4.6 feet down) the forecaster digging the pit felt his foot break through into the weak layer and a large collapse was triggered.

Cracks shot out from the pit across the entire slope and this deep slab avalanche released in steeper terrain, 500' to the E along the ridge.

[bodywhomper]

thanks for starting the thread. the facet layer seems pretty widespread, based on the observations from the avi center. it will be interesting to see observations after the upcoming small wind event, followed by mild weather, followed by the storm event forecasted for next week....

[meter-man]

DPS are always a problem, no matter where they are found. Seriously, those skis fucking suck.

[bodywhomper]

Have some more koolaid!

[bodywhomper]

with the large new load in the tahoe area, the avi center added the PWL back into their advisory. i'll be interesting to see if anything rips big. i hope peeps are making good decisions today....

[SchralphMacchio]

with the large new load in the tahoe area, the avi center added the PWL back into their advisory. i'll be interesting to see if anything rips big. i hope peeps are making good decisions today....

I didn't expect anything else besides DPS being added as Problem #3 today, and through the weekend, with the way these recent storm waves had come in to Tahoe.

1. PWL existence and propagation potential was not completely ruled out of 100% of Professional Obs in the week leading up to the precipitation event; therefore evidence of existence is confirmed, even if distribution is potentially low, and also certainty of trigger possibility and/or likelihood is unknown ...
   See this ob from Carson Pass 3/15 indicating propagation potential (https://www.sierraavalanchecenter.or...elephants-hump), even if other obs from the region showed unlikely propagation potential, reasonable uncertainty could be expected on a given slope of choice without having multiple obs from that specific slope that rule out likelihood of PWL existence/prop potential.
2. Roughly 8" of new SWE in 72 hours across the region
3. Sustained SW winds leading to cornice growth and windslab development, also known as massive F'ing trigger potential that could possibly be overlying remaining PWL (wherever it may exist)

My forecast conclusion: Possibility of potentially historic sized avalanche, likelihood low and contained to specific areas within the forecast region, overall uncertainty high (unless it is specifically known that certain slide paths had already failed on that layer and/or completely rounded to the point that triggering with a massive load is not practically possible)

My practical touring conclusion: I would not be fucking with any slopes below cornices or windslabs this weekend, *even if I am below treeline, because the upper slope failing could eat the trees like toothpicks*, unless I had personally seen the old crown and track on that specific path.

I also happen to be back in town with my touring gear (which, admittedly, might also be too skinny for me to practically enjoy for the kinds of low angle terrain where overhead exposure of cornices or windslabs does not exist)

[LightRanger]

My new Helio 116s are the win for these kinds of days. :-)

[bodywhomper]

schralp, i can't tell from your tone if you are lecturing me or not, hopeful not.

My new Helio 116s are the win for these kinds of days. :-)

i go even bigger! big R/R skis, for me work well even in low angle, deep snow, dense trees.

there are some super fun zones that did not have the facet layer that are very skiable now because they did not have snow when the layer formed.

if we get a BIG cycle, maybe we'll get some new lines to enjoy in the future ala trimmer peak.

[SchralphMacchio]

schralp, i can't tell from your tone if you are lecturing me or not, hopeful not.

I’m not lecturing you (I know you’ve been in the game longer than me), more so working out on paper my own thought process about the situation ... Because my partners and I were literally having a text convo all day about the Avy problem and where to tour tomorrow. I’m back in town from Oregon for this weekend only, planned it well before the dump was forecasted!

[bodywhomper]

It looks like you all had a good and incident-free tour

Sent from my SPH-L710 using TGR Forums mobile app

[TahoeJ]

So Schralph - where did you guys end up going in these high conditions over the weekend?

[SchralphMacchio]

We did have an awesome, incident free ski weekend! On Saturday we kept it low angle (stayed at or below 30 the entire day) and away from overhead exposure to windslabs/cornices. Needed to see first hand what was going on with storm slab before committing to steeper lines with slide potential - consequences just too high to choose terrain where we could end up in small paths or traps below treeline by accident - even a 40’ wide slide path would be unsurvivable if it failed on all 5’ of new snow and you get flushed into a tree or terrain trap.

Honestly though after seeing the consolidation and settlement on Saturday and no propagation characteristics within the new snow I think the biggest hazard over the weekend, below treeline, was treewells. We found some truly terrifying air voids barely covered by snow in the BC in Saturday and worked that into our descent plan for Saturday and today.

For today we increased the slope angle to 35-38 but stayed off solar aspects and far away from any cornices. The windloading seemed to hit really hard up by Squawlpine/Anderson etc, but much less so in other areas with other mountains to the SW (breaking up the flow). Pretty much skied northeast aspect all day with zero wind effect.

I was talking to my friends about the DPS problem being removed today. No new obs involving failure on that layer, 48 hours after the most serious loading, warmish snowpack temps today ... and yet in very isolated and extreme terrain I bet the problematic interface exists and is triggerable by a massive load such as a windslab or cornice failure ... but if the probability is so low I guess you have to pull it from the problem list. With the warming, consolidation, and cooling coming soon I personally don’t see that layer becoming active unless a 15’ tall cornice drops onto a massive north facing path that hasn’t warmed up yet.

[jorion]

So Schralph - where did you guys end up going in these high conditions over the weekend?

I was curious as well.

It doesn’t seem like he wants to disclose!

[panchosdad]

So what does DPS stand for anyway? Deep Persistent Shit?

And those skis suck.

[SchralphMacchio]

I was curious as well.

It doesn’t seem like he wants to disclose!

I skied north and northeast terrain all weekend, near and below treeline, never under overhead exposure from windslabs. Slope angles previously disclosed, very low terrain complexity.

As far as decision making goes, that’s all the relevant information needed!

[Nkane]

Someone got the deep slab to go on Houghton yesterday: https://www.sierraavalanchecenter.or...bc-mt-houghton

[meter-man]

Someone got the deep slab to go on Houghton yesterday: https://www.sierraavalanchecenter.or...bc-mt-houghton

I don't think that's the DPS problem identified above. That looks like it only slid 4-5 feet deep at the crown - i.e., all storm snow. The March 3/4 DPS problem was already at least that deep before this storm cycle - it slid on a layer 4-8 feet deep. If it was the DPS discussed above, it would have had to slide on a layer about 8-13 feet down - a WAY bigger slide. So says this non-pro-forecaster from the comfort of my internet-viewing chair.

That said, this one seems to be a new deep instability. Joy!

Overall, I was really surprised by the lack of avalanche activity over the last few days. Warming may change things today, but the rain Tuesday/Wednesday will almost certainly get some things moving.

[SchralphMacchio]

I don't think that's the DPS problem identified above. That looks like it only slid 4-5 feet deep at the crown - i.e., all storm snow. The March 3/4 DPS problem was already at least that deep before this storm cycle - it slid on a layer 4-8 feet deep. If it was the DPS discussed above, it would have had to slide on a layer about 8-13 feet down - a WAY bigger slide. So says this non-pro-forecaster from the comfort of my internet-viewing chair.

The party that triggered it, and had the best view, also concurred with that assessment, based on the data in their observation post. Another thought, that E face gets a lot of sun, possibly not a prime candidate for the NCF interface leading to the DPS problem of note in the original thread post (I'll admit I haven't been poking around Tahoe in person at the NCF layer to see what kind of crust it formed on/under, just assuming it's less likely on solar aspects).

That said, a 4 foot slab is a 4 foot slab - traumatizing at best and unsurvivable at worst.

[meter-man]

That said, a 4 foot slab is a 4 foot slab - traumatizing at best and unsurvivable at worst.

Damn right!

[TahoeJ]

I was curious as well.

It doesn’t seem like he wants to disclose!

It was the West Shore, I'm pretty sure. Jakes?

No need to be elusive, there are only so many places you can actually park these days. ;-)

[mcski]

He mentioned parking in the other thread. There aren't that many options so I'm not sure why he doesn't want to say as he already said he parked in one of legal spots?