Wednesday, February 3, 2010

The Persistant Weak Layer (PWL)

The last week and a bit has allowed me some time to escape the wilds of BC to journey down south to UT. Meetings with the AMGA (American Mountain Guides Association), a visit with my parents and catching up with good friends before I return to my semi-hermit existence at my backcountry lodge in British Columbia Valhalla Mountain Touring.

The last 10 days skiing around Utah has been eye opening - 3 avalanche fatalities in the super dicey snowpack that has seasoned avalanche veterans running scared, and cocky locals pushing the limits. The situation in Utah is this: some early season snow sat around in the hills for weeks of high pressure. This created an extremely weak and faceted snowpack that was then pummeled by up to 80" of snow just over 10 days ago. Huge natural avalanches were popping out all over. Ski patrollers were getting caught in bounds, a few unfortunate people lost their lives. But all the while people are skiing in some wild places, pushing the boundaries of what is safe, and maybe even getting away with it. What gives? What is going on? Is it safe out there?

I have alot of thoughts on the topic, as I am an opinionated, IFGMA Mountain Guide and former avalanche forecaster. I know that I am very conservative, but I have also skied my share of big lines in big committing places. The difference I guess is that I have time on my side - I spend around 120 days a year ski touring. I get my fix, my itch is scratched. But when I come down to UT and see what people are skiing with the snowpack they have, it gives me the chills. The problem right now is that we have what is called a Persistent Weak Layer. This faceted snow at the base of the snowpack isn't going anywhere, and it isn't going to heal very quickly either. People may think it will, but if there is one thing I have learned from my time in the hills, it's never, EVER trust a PWL. They stick around, (hence the name Persistent) and just when you least expect it, WHAM! You are in a big avalanche.

And right now is the time in UT that kind of scares me the most. Avalanches have stopped being triggered on a daily basis, there is no new significant loads, people are starting to ski in more radical terrain, but the PWL is still there. The shallow trigger points are out there, just waiting for the 3rd, 10th or 75th skier to hit the sweet spot and pull out a large unsurvivable avalanche. Yikes. Bruce Tremper had a quote in his "Staying Alive in Avalanche Terrain" book that has stayed with me for years now. Since I don't have the book in front of me I will paraphrase. Basically he said if are 99.99% certain that a slope is not going to avalanche, and you ski 1000 slopes with that confidence, then you will get caught 1 time. If I ski a big avalanche slope every day I go out skiing (some days I don't ski any, some I ski quite a few), than that means once every 10 years I will get caught. If I have a 40 year ski touring career, I will get caught 4 times. I don't like those odds. And skiing in avalanche terrain right now in UT is like trying to beat the house in Vegas, but the dice are loaded in the house's favor just slightly.

Part of the bigger picture problem in UT is that skiers here don't regularly ski in a PWL snowpack. The central Wasatch is host to a pretty forgiving snowpack, with the avalanche danger usually associated with new snow wind loading. The PWL doesn't live here very often, it usually just stays at home in places like Colorado. Coloradans are well trained in dealing with the PWL, and they skip through powder meadows, ski the trees, and generally just bide their time until late March/April when the spring conditions start to settle things out. So some folks have stopped seeing slides and are starting to go for it. Maybe an old slide path that has already avalanched is safe - but maybe not. Stop and dig on the reloaded bed surface and see if that PWL is still hiding out.

For now, while I am in UT, I am skiing like a Coloradan. Skiing dust on low angle crust on south aspects during or right after a storm. Steep skiing is confined to TIGHT trees, where on north aspects the powder is soft and deep. LAB (low angle bull sh*t) is the story on sheltered and shady terrain, where I am still having fun, traveling through the hills and staying fit.

Stay safe, dig around, learn about the PWL, and respect it before it schools you.

Kathy proves you don't need to be in the gnar all the time to have fun.

LAB skiing in the sun, so lame, why bother?

It might only be 30 degrees, but the sun was warm and the cold smoke kept getting in my face.

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