[tele.skier]

a few things...

If you don't ski when it's considerable avy rating in the PNW, You rarely ski and when you do, it's bulletproof...

I skied snoqualmie pass both saturday and sunday.

My observations during the storm saturday was that there was significant wind for a few hours during the storm above 4000 ft. On certain slopes there was scouring and wind transport, depending on the direction they faced. On other slopes not so much

The obvious danger was the weight of the new snow and whether older, persistant weak layers were bonded (which turned out not to be the case) The less obvious danger was, the marginal, but significant wind above 4000 ft. saturday during the storm that subsided long before the snow stopped falling. The resulting localized windslab was burried in an unscoured blanket of blower pow. (blower by PNW standards at least)

Alpental's pro patrol bombed the hell out of alpental sunday. The main lift didn't start running until 9:45am. They weren't taking any chances, but patrol has the benefit of a manned observation shack at 5000', so they saw trouble developing and rightly (in hindsight) were extremely cautious, bombing the hell out of the place.

There's so much to potentially discuss, There's so many factors that marginally existed that could have contributed to the cause of this tragedy.

I didn't go into the backcountry that day, but I wish I had dug a few pits, so I would know if I would have noticed any signs of significant danger myself, and been inclined to meadow skip low angle from my observations,..... or would I have seen nothing alarming and gotten caught myself.... None of us know can know this.... and probably hope never to know this kind of thing.
_________________
the fall line is your friend.... resistance is futile

[Doug G]

The random component in avalanche hazards seems particularly strong, compared to, say, skiing trees without hitting one. Which means you have to have a particularly huge margin of safety, I guess.

[billk]

[Rebob]

[billk]

[ghostofcarl]

[Rebob]

billk wrote:

[billk]

[stevesliva]

I'm new here, but it sounds about right to me. Conditions seem to be, in general, "go tour or you'll miss it."

[Mr. T]

So part of the issue is teasing information out of the "considerable" rating, and that has always been subject of discussion. Is it more likely that in a "considerable" condition, variations of stability in snowpack with slight changes in aspect (spacial variation?) become more problematic than in say, a "high" rating where there is more caution practiced by parties?

What is the rating associated to the highest number of human triggered slides (bigger than sloughs)?

[Mr. T]

[hutguy]

As Mr.T says, touring for turns during considerable danger itself isn't the issue. Terrain choice and management is. It all comes down to your parties level of acceptance of risk. How your party assesses that risk has to do with the level of education and/or experience.
_________________
Creeds and doctrines are like a raft to get you to the other shore and then to relinquish. Neither cling to the raft or reject it when drowning. Even better, become a strong swimmer.

Shakyamuni Buddha. The diamond sutra

[sandy]

Most accidents - at least among those reported - happen when avalanche hazard is considerable. People think the danger scale is linear, but, most avi pros think of it as exponential - that is, considerable is several orders of magnitude worse than moderate, not just one step up the ladder (http://avalancheinfo.net/ADFAR%20Proj%20Docs/CAAAvalSocScienceStudyBrief.pdf).

Personally, I think y'all are over thinking this. Apparently, there was 65 cm of new snow in the previous 48 hours, much of that falling in the 24 hour period between the 18th and 19th - accompanied by moderate to strong SW winds. There was a buried surface hoar reported extensively in the area, including on S aspects. That is a big load to rapidly dump on a weak layer, and we know from dozens of previous studies that facetted crystals (ie. depth hoar, surface hoar or near surface facets) are responsible for most slab avalanches.

Numerous skier triggered avalanches had been reported in the previous 24 hours showing that the storm snow had formed a slab and was touchy. There were even step-downs to the surface hoar reported.

Shear stress on a slope rapidly increases past about 37 degrees, this group was skiing a 42 degree slope, that, from looking at the google earth picture of the area, had a high likelihood of being cross-loaded. They were above numerous nasty terrain traps.

Take a big load, stack it rapidly on a weak layer, add a lot of shear stress, some cross-loading, load the snowpack rapidly again with a skier. Not so surprising that an avalanche occurred.

[stevesliva]

Why do so many around here sound surprised, though?

[Rebob]