karlo

Out on the slopes
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Thanks.

So, this avalanche at Silver Mountain Resort was a skier triggered large avalanche,


Avalanche
  • Type: SS
  • Trigger: AS - Skier
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D3
  • Sliding Surface: O - Within Old Snow
Site
  • Slope Aspect: E
  • Site Elevation: 6200 ft
  • Slope Angle: 35 °
  • Slope Characteristic: --

Size details, “The avalanche released about 90 feet below a corniced ridgeline on a buried layer of surface hoar. The crown face was about 2 to 3 feet deep and 300 feet wide. The avalanche ran over 900 feet downhill and about 450 feet vertically.”

Size classifications,https://www.slf.ch/en/avalanche-bulletin-and-snow-situation/about-the-avalanche-bulletin/avalanche-sizes.html

I don’t recall the source, but I recall reading that there were three unintentional avalanches there that day. I think that means the avy hazard was at least Level 3, maybe Level 4 on account of there having been three avalanches. Reference here,


From the same page, “Every modern ski resort will issue notices (bulletins) indicating the level of Avalanche Risk for each day.”

This was apparently in a more remote area of the resort, Wardner Peak.


I wonder what Avalanche Risk level Silver published for Wardner Peak area.
 

New2

Getting off the lift
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May 3, 2017
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Jwrags

Aka pwdrhnd
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Nov 17, 2015
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378
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Portlandia
Not sure where to post this but found it interesting. Mt. Bachelor just finished a huge snow cycle and when they get the NW Express lift open they are implementing the following


  • When Northwest opens, mandatory buddy riding WILL be required in the West Bowls. What this means is Ski Patrol may be checking buddies at entry points to West Bowls. If you exit a run and lift without your buddy we will be checking in on what happened, and you may / may not be able to load the lift until buddies have been reconnected. Be smart, be safe, be cool, stay stoked.“
I have never heard of this before but it seems like a good idea.
 

karlo

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Update from the Spokesman-Review: Skiers triggered deadly Silver Mountain avalanche despite best efforts of ski patrol, preliminary investigation says
I think the Idaho Panhandle Avalanche Center handles publishing risk level for Silver, Schweitzer, Lookout, and Turner, rather than the individual resorts/ski patrols. The whole region was flagged Level 4 High Risk - Red.
@Unpiste pointed that out too, that risk assessment for the region does not apply to a resort. It’s still interesting to see to what degree the Avy Center’s assessment applied in this case. They do have a reported observation from near Wardner Peak Traverse,
https://www.idahopanhandleavalanche.org/observation/snowpack/2019/dec/28/extended-column-testing-rutschblock-site-1222
Not sure if the observation was on 12/22 and reported on 12/28, or if it was on 12/28. I wonder if the surface hoar observed is the same layer noted in the Spokesman Review article. For those unfamiliar with what surface hoar is, check this out,

http://cbavalanchecenter.org/what-is-surface-hoar/

The photo tells it all. Though the crystals compact and change, if there, it’s still layers and layers of newer snow on stilts, on a “persistent weak layer”.

There were three advisories that morning. The relevant one?, for Silver Valley, is here,
https://www.idahopanhandleavalanche.org/advisory/2020/jan/7/2020-01-07-054957-avalanche-advisory#null
The presence of persistent weak layers is noted. And, if resort mitigation and skier traffic is dealing with the persistent weak layers, then it’s a different ball of wax. If not, then the regional assessment might be very applicable. I would still be interested in knowing whether or not, as the j2ski.com page says “modern” resorts do, Silver Mountain Resort published a risk assessment for Wardner Peak. If so, from what observations, collected over the season, did they make that assessment.

SR article: “
in addition to the specific mitigation techniques used and decisions made, will be released by Silver Mountain some time in the “next couple weeks,” said Silver Mountain spokesman Gus Colburn.

Decisions are based on assessments.

The article speaks of the crown location and that it was skier triggered. More details and photos are in the
CAIC report found here,
https://avalanche.state.co.us/caic/acc/acc_report.php?acc_id=731&accfm=rep

BD3F1A88-7AC5-4C1D-8C36-ED9D6341E9FD.jpeg
4B3B02DD-E058-476D-8C0C-410B14FC520F.jpeg

Looking at the trail map, the photo, and with my understanding of where the skiers were (on 16 to 1, coming off Wardner Peak Traverse), am I correct that the skiers were well below the crown of the slide? If so, though skier triggered, it didn’t take much to trigger. ! I.e., it’s not like anyone skied where the crown is. And, per the SR article, the weak layer was deep, so also old. Could it really be that weak? Guess so.
 
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