Forum Index > Trail Talk > Well goodness, it may snow, avalanche hazard
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moonspots
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Happy Curmudgeon
PostFri Dec 14, 2018 12:22 pm 
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gb wrote:
Also check the forecast levels in the Avalanche Forecast

Do you know why the old tri-colored avalanche rose displays are now just grey/black? Is it their website (or my goofy MacBook perhaps) do you think?

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"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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North Cascades
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PostFri Dec 14, 2018 2:08 pm 
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It's their website.  They are grey/black on my pc as well.
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hbb
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PostFri Dec 14, 2018 5:42 pm 
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Most organizations moved away from using the danger scale ratings in the avalanche rose format. NWAC had a blurb about this when they made the change, which I can't seem to find, but here is an explanation from another forecasting group:

https://www.sierraavalanchecenter.org/what-happened-danger-rose
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moonspots
Happy Curmudgeon



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PostSat Dec 15, 2018 11:14 am 
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hbb wrote:
Most organizations moved away from using the danger scale ratings in the avalanche rose format. NWAC had a blurb about this when they made the change, which I can't seem to find, ...

So that's it. I'm still not sure what the "problem" with the danger rose was, but so be it. I thought it was quite informative, the new method being more generic, therefore less useful. It doesn't really matter anyway, as I rarely venture into avalanche territory.

Thank you for the information.

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"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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Get Out and Go
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PostSat Dec 15, 2018 9:44 pm 
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Typical Mt. Baker fashion, in one week the ski area went from not being open with 13",  to the highest base total in North America, with almost 90".  (BTW, after 2 winters working at Stevens Pass my son has now moved on as a ski instructor at Baker.)   bricks.gif smile.gif

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gb
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PostSun Dec 16, 2018 12:35 pm 
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Mussentuchit until after Thursday when things finally calm down and cool off.

Fun: NWAC:
Quote:
4) Wide shot of same avalanche crown running from High Pass to Low Pass (red line defines crown - measured on Google Earth at +3000' wide). #cascadewestnorthbaker #nwacobs @k2skis @msr_gear
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gb
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PostSun Dec 16, 2018 12:40 pm 
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As is typical for these types of events the hazard is region-wide.

Canadian Avalanche Association Avalanche.ca:

Quote:
Special Public Avalanche Warning

BROUGHT TO YOU BY
Yamnuska Mountain Adventures
DATE
THURSDAY, DECEMBER 13, 2018
Warning applies to most mountainous regions of BC

Special Public Avalanche Warning for Most Mountainous Regions of BC

Dec 13, 2018, Revelstoke, BC: Avalanche Canada is issuing a Special Public Avalanche Warning for recreational backcountry users, in effect immediately until the end of day Sunday, December 16. The warning applies to the following forecast regions: Lizard Range and Flathead, Purcells, Kootenay Boundary, North Rockies, South & North Columbia, Cariboos, Sea-to-Sky, South Coast, South Coast Inland and Northwest Coastal. For a map of the regions involved, click here.

After a prolonged drought in late November and early December, the province has been hit with a series of storms that have dropped a significant amount of snow. This new snow is not bonding well to the old surface that formed during the drought.

“Our main concern is that we are expecting the weather to clear on Saturday,” explains James Floyer, senior avalanche forecaster for Avalanche Canada. “After all this rain in the valleys, backcountry users are going to want to hit the alpine but that’s where the danger is greatest. There’s a very weak layer now buried anywhere between 60 and 150 cm. Any avalanche triggered on that layer will definitely be life threatening.”

Avalanche Canada warns anyone accessing higher elevation terrain to be aware of this hazard. This means skiers and boarders leaving ski resort boundaries and snowmobilers riding at or above the treeline. Everyone in a backcountry party needs the essential rescue gear—transceiver, probe and shovel—and know how to use it. And always check the current avalanche conditions at www.avalanche.ca.
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thunderhead
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PostMon Dec 17, 2018 7:17 pm 
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Story just popped up on TAY... dude took a ride on a slab in the crystal area BC.  Was ok but it sounds like that recent weak layer is still there.  It might be deep enough now that unless it has recently slid, the new rain wont touch it above a certain elevation...
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gb
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PostTue Dec 18, 2018 7:43 am 
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thunderhead wrote:
Story just popped up on TAY... dude took a ride on a slab in the crystal area BC.  Was ok but it sounds like that recent weak layer is still there.  It might be deep enough now that unless it has recently slid, the new rain wont touch it above a certain elevation...

That is the problem. When one looks at telemetry for Green Valley and compares that to telemetry for the base of Crystal for the day before yesterday, you can see that a fair amount of water was measured at the base - .7" beginning around 11 AM- while only one inch of snow appeared to have fallen at Green Valley, yet the summit of Crystal was around 31 to 32F maximum. So, there should be a crust up to some unknown elevation between Green Valley and the top, but perhaps above that not enough of a crust to make triggering the weak layer unlikely. The same is true at Stevens perhaps around 4800' (from telemetry). In addition to the snow/rain elevation, along the crest of the Cascades and the east slopes there really had as of yet not only not been enough warming but there also hasn't been enough snowfall to deeply bury the weak layer, making it harder to trigger. But today is a different story with heavier snowfall along the east of the crest areas and it should be likely that the storm loading would make it more likely that the weak layers would get stressed to the point of failure. Avalanche hazard in these areas today should be higher once again not only from the storm but also from the persistent weakness.

Meanwhile, west slope Cascades have had a good deal of heavy snow and also have received a fair amount of wet snow/rain up to 5000' +- in the North (Baker) and 6000'+ in the south (Paradise). It looked for instance that a day and a half ago Baker at the lodge got 2" of rain. The problem in these areas should relate more to the usual storm loading scenarios as in today and again on Thursday.

In most places in British Columbia on the other hand, the problem could get worse for a while near storms as a gradually more cohesive slab forms on top of the weakness and in most places is not yet deeply buried. Submitted reports from British Columbia make interesting reading. It is interesting to note how most recreationalists appear to be making good decisions while a few have not: https://www.avalanche.ca/mountain-information-network/submissions To me it is surprising that no one has yet been caught in a fatal avalanche (particularly in BC).
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thunderhead
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PostTue Dec 18, 2018 8:43 am 
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Hyak was CROWDED the other day.  So ya, lots of people are worried about whats up high, and rightly so.

Last nights storm came in significantly colder than I expected... more snow and less rain.  I think somewhere in the near treeline band and above we might have a PWL for a long time...
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PostWed Dec 19, 2018 12:18 pm 
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The most recent report of a slab failing on this layer was from December 18th at Crystal Mountain, when an small explosive released a very large avalanche during control work. A ski patroller was caught and carried, but remarkably sustained very little injuries. The avalanche was large relative to the path, and large enough to bury several buildings.  It occurred on a Northwest aspect at 6600ft

-From NWAC today.


eek.gif

That sounds scary.  My question is what part of Crystal faces NW at 6600 feet.  Do they actually mean NE?  Something across the valley in the side country... but what buildings would it have hit?
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PostWed Dec 19, 2018 3:20 pm 
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Maybe they meant that as a simple comparison, IE, D4, and not that it actually hit any buildings?
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gb
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PostWed Dec 19, 2018 8:28 pm 
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Meanwhile, in the Canadian Rockies it looks like one can get good safe skiing if you keep the angle under 20 degrees. cool.gif https://www.avalanche.ca/map?panel=mountain-information-network-submissions/45c54741-c6f7-441c-b840-b91a2b255463
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gb
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PostWed Dec 19, 2018 8:31 pm 
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thunderhead wrote:
Maybe they meant that as a simple comparison, IE, D4, and not that it actually hit any buildings?

I am sure they meant could have destroyed several buildings. Don't know Crystal well enough anymore to think of a NW aspect at 6600'.
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PostThu Dec 20, 2018 2:33 pm 
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On the east side it's "I am not quite done with you yet."

NWS:
Quote:
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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