Late Spring/Summer Avalanche Hazard

Thanks very much to everyone for the tips - it's great to be able to tap into so much collective experience on a site like this. I just reserved a copy of the Tremper book and am going to need to make the time for the 3-day course next year.

A question on the snow temps - what is the best method to measure these? Would you push the thermometer down into the snow overnight, and then take the reading in the morning? Does 20 cm refer to the depth of the measurement?

Cheers,
David

Although I'm sure there are exceptions, I think there's a pretty strong correlation in spring between good skiing conditions and safe skiing conditions. When you're on firm corn snow and you're only sinking in a little bit, I think it's usually pretty safe. On the other hand, when the snow is sloppy gumbo, the risk of avalanche is higher.

The key exception I can think of is when the snowpack is not really isothermal yet (generally earlier in the spring). In this case, you may have a good supportive crust after a cold night, yet there can be weak layers persisting underneath. One time I observed this was during a tour from Rainy Pass to Heather Pass (North Cascades highway) several years ago. As I was climbing the south facing slopes toward Heather Pass on a supportive crust, the slope started whumping. Spooky! I moved to the colder north facing slopes on the other side of Lake Ann and enjoyed good skiing on that side. It was powdery there as I recall.

Lowell & Gary's comments on ski penetration are a good way to evaluate late-season hazard on the spot. David, your original post shows that you're well aware of the importance of trip planning/ time management, but for an excellent further discussion, check out Ch 2 in the new "Backcountry Skiing..." by Martin Volken, et al.

As for your questions about the thermometer: yes, the 20-cm refers to the depth & it takes only a few minutes to get an accurate reading. Life Link includes these in their snow pit kits, but they seem spendy to me. (Anybody know a cheaper source?) I'd recommend attaching a bit a bright flagging so you don't lose or step on it while skinning up/ getting ready. They're pointy & fragile, but you can make a nice sheath from a scrap of plastic pipe.

If I remember correctly, a reading of 0*C means the snow is saturated with free water. With a high reading at the start of the tour, you'd probably want to adjust your plan, especially if you're doing a loop or traverse where it's more difficult to just back off if the snow starts to change quickly.

"Uber-cautious" is OK, after all, it's your game-your rules. IMHO, risk is relative, and most people, on most days, are at greater risk driving to & from the snow than playing on it. Good luck & Happy Trails!

Great information; I'm glad to see some attention to the subject. DG- I'm looking to take an avy course next season as well. I heard that Mountain Madness offers a good course...

One more thing to look out for in the spring is falling cornices. There are some biguns this year. Sometimes they just melt away, but hot days can let some of em loose, which can enchain the slope below, creating quite a slide. Try to avoid climbing up directly under them, or walking out on them, especially latter in the day. Check out the one right of the summit on Mt. Pilchuck (picture taken 5/1/08).

By the way, doubt many folks will be under that one very soon. The road is still gated and covered with snow, so you have 6 miles of road to get to the trailhead.

Great comments from all, especially the pros like Gary and Lowell. One other thing that comes to my mind from personal experience (another term for "mistakes I've made") is that there are times when the surface will wet sluff as you ski, fairly shallow and manageable and fun to ski on . However, as the day goes on the confidence and comfort of the group tends to go up as the fun progresses, while the depth and ease of sluffing, along with the volume of entrained snow and the lubrication of the sliding layer (speed of sliding entrained sluff) goes up as well. This can come to a very sudden bad turn when the now very comfortable group drops into a steeper warmed feature, accompanied by the bad things: recent storm loading, bad stuff below you to get carried into, and that classic spring fun feature of banked sidewalls like a halfpipe that are fun to carve rail to rail, sluffing the whole width of the couloir. Surface sluff is fun and manageable until it's not - then you're on your face going downhill fast toward the cliff band. I have to remember this one as the day progresses to keep it super fun in the sun all the way back to the lawn chair, cold beer and smoked oyster. Oh yeah - pass me back that SPF 70.