NW Alpha angle or runout angle

www.wildsnow.com/10011/alpha-angle-avalanche-safety/

I just spent way too long enjoying the above post on wildsnow, especially the comments. It got me to wondering if there was a different runout angle used in the NW. I seem to see anywhere from 18 thru 20 something thrown around but wondering what the local experts keep in mind for our snowpack.

I have never gotten too technical about these things and usually just eyeball angles but they are often on my mind when setting an uptrack.

The comments of the post brought up some fun to think about things such as slides that went up hill on the other side of a valley.

Great question and a nice article.
Some folks like to use odd numbers...19, 21, & 23, when thinking of Continental, Intermountain and Maritime snow climates.
So that's 19 for Continental, 21 for Intermountain and 23 degrees for Maritime.

A modified version of what I'd said on Lou's page in the Spring:

It looks like the most widely-cited paper on the subject is authored by McClung, Mears and Schearer, from 1989. (two links for paywall redundancy)

www.igsoc.org/annals.old/13/igs_annals_v...ar1989_pg180-184.pdf
archive.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc31059/nrcc31059.pdf

The paper quotes alphas of 29.4±5.2 degrees for Western Norway, and 20.7±3.9 for the Sierra Nevada, the two maritime examples in the paper.

In this context “± 5.2″ and “± 3.9″ is a single standard deviation. If avalanche alpha angles are “normally distributed”, in order to avoid 95% of slides, you’d need double that to 29.4±10.4 degrees and 20.7±7.8 degrees, respectively. Particularly telling is the range of values that are quoted. They observed alpha angles ranging from 14 (Sierra) to 42 (Norway) degrees.

Tread carefully if you're making decisions regarding alpha angle at the level of a couple of degrees' precision.

Thanks for the input. It makes sense that it would be greater but I wasn't sure by how much. No worries about my level of precision being that close. When I am making good decisions, I try to factor in at least that much caution. I like the idea of breaking down some of these concepts into terms that might be more accessible to more people like they did.