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gb
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PostThu Dec 20, 2018 1:33 pm 
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On the east side it's "I am not quite done with you yet."

NWS:
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We have an inherently weak snowpack structure in the East Cascades. The weak layers themselves have been identified as buried surface hoar and/or buried near surface facets, and appear to be blended into the form of basal facets and even depth hoar as one moves further east, or up in elevation. This layer is dated to December 9th, when it began snowing after a prolonged early season drought. Basal facets have been observed in the Wenatchee Mountains, the Stuart Range, the Chiwaukum Range, and near Washington Pass. In short, it is a poor structure and one in which it will be hard to develop confidence in for some time.

In Icicle Creek on December 19th, I spotted a number of very large avalanches that likely occurred mid storm on the 18th. These were on a variety of aspects and elevations as low as the mid 5,000ft range. These slides were impressive, and filled in the tracks of some large slide paths. One recent explosive triggered slide at Mission Ridge stepped down to basal facets near the ground, resulting in a 20” to 40” deep crown that propagated approximately 120 feet wide. The continued loading from snowfall and strong winds will add to an already stressed lower snowpack. An old professor of mine used to say “Faceted grains are strong in compression, but weak in shear.” They can hold up to an enormous amount of weight, but when they do fail, wide propagations can be expected.
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Schenk
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PostThu Dec 20, 2018 2:01 pm 
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Thank you GB, and Merry Christmas to all

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Nature exists with a stark indifference to humans' situation.
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gb
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PostSat Dec 22, 2018 5:58 pm 
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With the new snow coming people are going to want to get out. But remember areas of the Cascades that have not had a significant amount of deposition over the weak layer may perhaps still be triggered by human travel. These are primarily east of the crest but extend to the crest at Crystal Mountain and likely Stevens Pass above a certain elevation and in many locations like the Teanaway, Chiwaukum, Nason Ridge, and the Stuart Range further east. During and shortly after storms additional loading could also result in dangerous natural avalanches.

Crystal Mountain is apparently taking this possibility seriously as they have not yet opened the North or South Back. A friend tells me that they announced on the website that they were using a helicopter to bomb certain locations today that put certain side country runs at risk. They also are warning skiers to stay out of the backcountry in no uncertain terms.

This from a NWAC report yesterday:
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Pro Obs December 21, 2018: Matt Primomo Northeast Cascades: Happy Solstice! Today we found more evidence of recent very large avalanches. This one below the north side of Silver Star Peak had crowns approximately 1.5km wide, spanning the steep slopes underneath rock bands of the massif. At all elevations we found persistent weak layers. At 4,000ft this was a thick layer of buried surface hoar. Above 5,000ft this was basal facets. Profile pic is from ESE at 6300ft, showing a generally stable structure with increasing hardness, except for the bottom 20cm. Pic 3 is large grained, striated basal facets found near the bottom of the snowpack at the same location. These were likely the culprit to the recent very large avalanches in the area. Tests showed the snowpack can still propagate fractures at both 4,000ft on N, and 6300ft on ESE. Follow along at www.nwac.us @k2skis @msr_gear @outdoorresearch #cascadeeastnorth #nwacobs

and:
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Professional Observation: December 20th 2018, Ian Nicholson Today while touring out in the backcountry we avoided traveling on and around large open slopes that were steep enough to avalanche. In fact when traveling at mid and higher elevations we made sure to give these big slopes a wide berth because of the highly destructive nature of the current deep persistent avalanche problem. This problem is due to weak snow; a combination of facets and buried surface hoar that exist just over three feet down in the snowpack. These weak layers have been the culprit in several very large avalanches that have been reported over the last few days. While some observations show this layer has been gaining strength, you may still be able to trigger it with large loads or at thinner locations in the snowpack. Any avalanche on this layer would likely result in a 3+ foot deep slab that would no doubt be disastrous Photo: @tinovillanueva sticking to lower angled treed slopes while in Commonwealth Basin on a damp and soggy Thursday. #nwacobs #cascadewestsnoqualmiepass @msr_gear @outdoorresearch @k2skis
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Triton
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PostSun Dec 23, 2018 10:50 am 
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gb, I'm assuming one can feel comfortable skiing inbounds say at Stevens???
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christensent
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PostSun Dec 23, 2018 5:45 pm 
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Triton wrote:
gb, I'm assuming one can feel comfortable skiing inbounds say at Stevens???

In general it is always "safe" to ski inbounds with regard to avalanches. It is a controlled space. Although people do on rare occasion get injured or killed in avalanches, you are pretty much trusting ski patrol to either make the area you are skiing safe or close the area if they are unable to make it safe. Even in the worst of avalanche conditions, they are out there performing one of these two tasks to ensure safety.

So ultimately, yes, you can feel comfortable skiing inbounds at any of the resorts.

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gb
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PostTue Dec 25, 2018 7:57 am 
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Here is a good summary of the current concerns from the NWAC: https://www.nwac.us/avalanche-forecast/current/cascade-east-north/#photos

There appear to be no significant recent incidents (except a 2' slab at Baker yesterday in new snow) regarding the weak layer; which is finally for now and in the absence of storms settling down not only here but also in SW BC www.avalanche.ca

The Canadian Rockies and likely some places in the Purcells are the outliers.
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gb
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PostFri Dec 28, 2018 6:43 am 
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Along the crest at higher elevations and east of the crest plenty of rain and then snow will increase the avalanche hazard and particularly going east is likely also to once again tick off the weak layer in the period Saturday through Sunday, and continuing into Monday. Because Saturday will suck, that day should not be relevant; but follow precipitation amounts, temperatures and the avalanche hazard ratings and details if intending to go into these areas Sunday and Monday.

www.NWAC.us
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gb
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PostWed Jan 09, 2019 8:57 pm 
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Although things have gone more normal here - read sucky wet snow and crusts - the weak layer is still creating some excitement in British Columbia and a fatal accident in Montana and another with severe injuries.

In those areas (and on the occasions when we experience similar) this is good advice:

Quote:
The day before yesterday an avalanche size 3 was triggered remotely by skiers from Molar's ridge. We suspect the avalanche ran close to the ground on the crust buried in late October.
We dug on a similar aspect and elevation on Rudi's ridge and got no results on snowpack tests.
Digging is probably not an effective way to learn more about this layer. The best way to manage this problem is with conservative terrain choices.
We had a good day skiing mellow trees.
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Forum Index > Trail Talk > Well goodness, it may snow, avalanche hazard
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