Late Spring/Summer Avalanche Hazard

Hi all,

As a relative newbie to b/c skiing, I'm uber-cautious about avalanches to the point of probably missing some good snow. But that's okay - I'm frankly scared stiff of the thought.

So, I've mostly resigned myself to chasing powder inbounds off the lifts during the winter and waiting until at least May for any real backcountry skiing, after the snowpack has settled out (note: this year being exceptional, maybe June). That being said, it's still hard to find information on the potential risks for late season (late spring/early summer) avalanches, even though I know they can occur. Most of the training materials talk about winter conditions (I have admittedtly not taken a field class yet).

So, I'd like to pose the general question about late season skiing:

If one is to watch out for placing themselves on seasonal hazards like thin snow bridges and cornices, and resigns themselves to skiing after

(1) the snowpack has gone through several freeze/thaws, and is likely isothermic and well consolidated
(2) there has been no significant recent rainfall (or late season snow)
(3) there have been clear conditions overnight to let the snowpack freeze
(4) and you get an early start and turn around before the sun loosens the surface too much, beyond the prerequisite couple of inches for some good corn skiing,

Are you generally safe to target steep slopes assuming the main threat is from solar warming of the surface? Or are there other avalanche hazards to look out for this time of year?

This is of course acknowledging the usual disclaimers that b/c skiing is unsafe and you can never know for sure - I'm just trying to get a better idea of what to look out for during the late season.

Thanks!

Take an avalanche class. Very generally late spring skiing is easier to figure out than a mid winter snowpack. But just remember it may take a long time for the pack to become isothermal and break down some of the "bad" layers. Spring slides that step down can easily trigger deep instabilities. As I remember May is a particularly bad month for avalanche deaths in WA, which surprised me when I first learned that fact. Skip E.

DG - there aren't many avalanche classses running this time of year, but the book "Staying Alive in Avalanche Terrain", by Bruce Tremper is a great start on the learning process. Snow pits are always useful but remember they can change remarkably by moving 50 ft, so making stability decisions based on one pit isn't a great idea. Just some more thoughts. Skip E.

DG, You've mentioned some good guidelines.

Probably in the spring to very early summer consolidation is the key. There are usually weak layers if there have been recent snows and if the trend is a warming one. That could be right after a storm or it could be a week or more after a storm if temperatures get too warm.

Most spring avalanche cycles are diurnal so how good the freeze is makes a big difference. During prolonged warming periods, however, older weak layers periodically rear their heads (as Skip pointed out).

The most effective observations include depth of ski or foot penetration, how good the overnight freeze is and surface roughness. If there are meltwater channels showing on the surface or if you see red algae or suncupping it may well be past the time of significant avalanching.

Couple of things I keep in mind:  TG problems are  more of a concern/ possibility in Winter on north aspects and in spring  "heads up" on south aspects (all this 'in general' as it is not an exact science...hence never stop observing and learning....) due to the possiblilty of rapid heating (things that happen quickly like solar raidiation/heat (or bombs! for instance as an extreme example....) in or to the snow pack often act as triggers, hence instability and possible slide action.

Those are great books to read for sure which I go through once in awhile.  I like to learn about the newest insights so as to add to my additional arsenal of information.

Good topic!  Thanks to all for posting.  DG, I think you're definitely on the right track, especially your points 3) & 4).  I'd also highly recommend Tremper's book; it's especially strong on field stability tests and human factors.

When I was a winter volunteer at Paradise back in the 70's, the weather data was not yet automated, so we had to phone the info to NWAC each morning.  I noticed a fairly strong correlation between the 20-cm snow temperature and wet slide activity in the Spring.  When the morning snow temps were cooler than about -5*C, slides tended to be uncommon, unless the Seattle high hit say 70*F after weeks of 40's & 50's.  The closer the morning snow temp was to zero, the higher the frequency of wet slides in early to mid-afternoon.

This is just one factor among many, of course, but consider carrying a dial stem thermometer to help quantify your decision-making process.  You might have to adjust the numbers a bit for elevations & aspects other than the 5-7K sunny slopes around Paradise.

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.

Peteboy, very well written and very good advise.I liked the way you described it. Been there!

I for one, also tend to be more cautious on S facing slopes as opposed to N facing during the early parts of spring as well.

There should be a major spring avalanche cycle persisting through the middle of next week. Very warm temperatures after prolonged much cooler than normal conditions and a lack of spring consolidation make a significant cycle a sure bet if the weather models prove to be right. Even the cooling on Sunday and Monday (with cloudy skies) will be a temporary benefit. Temperatures at altitude look to be warm again on Tuesday into Wednesday. For at least a couple of weeks the warmer it gets and the longer it stays warm the more significant the cycle will prove to be. I'd guess that in some areas the February crust bond will get tested, meaning that some avalanches may involve all of the recent snows (March, April, May) down to the more consolidated early season snowpack.

Gary or others, in consideration of Gary's ominous forecast, do you have advice that is specific to the Easton Glacier route on Baker? We have a planned trip where we are expecting to set out from camp somewhere above 6k at about midnight Saturday with a target summit time of between 6 and 7 AM Saturday.

Interesting discussion, one that I was considering while touring this last weekend.

I seem to remember some early season concern that the ugly snowpack we were getting (weak layers buried under copious new heavy snow) at the time would end up being a problem come spring.

As I was cruising up a slope where a huge cornice bomb had previously impacted I was trying to imagine the that slope releasing and stepping down to a deeply buried layer- it boggles the mind to think it could rip down deep in what seemed to be a fairly consolidated pack. but i guess if it's a couple feet of consolidated snow that would be a great slab if there was still some of those crappy layers beneath.

Anyone care to comment?

I seem to remember some early season concern that the ugly snowpack we were getting (weak layers buried under copious new heavy snow) at the time would end up being a problem come spring.

Here's a link to last January's discussion about potential spring hazard. I let my imagination run wild regarding the worst-case scenario for spring avalanches here . I don't know if you'd call this week's situation worst-case, but it is interesting.

Gary or others, in consideration of Gary's ominous forecast, do you have advice that is specific to the Easton Glacier route on Baker?  We have a planned trip where we are expecting to set out from camp somewhere above 6k at about midnight Saturday with a target summit time of between 6 and 7 AM Saturday.

I won't predict whether you could ski the Easton Glacier safely on Sat-Sun. I'm reluctant to offer that advice here.

But I'm certain that if you'd like to climb and ski Mt Baker with good corn snow, it would be better to go later in the spring.

I had forgot about the January discussion. If I remember right, it was shortly after that discussion, maybe early Feb, when there was a warmer cycle that brought some big slides and all the highways were closed. After that period settled down I relaxed a bit about the buried layers and skied more open slopes than I had earlier in the season. The warming this week is dramatic so it will be interesting to see if any of the week layers remained a problem after those climax slides in Feb.

Here's a link to last January's discussion about potential spring hazard. I let my imagination run wild regarding the worst-case scenario for spring avalanches here . I don't know if you'd call this week's situation worst-case, but it is interesting.

I'd guess those predictions you made last January may prove rather accurate.  may be a good wknd for other outdoor activities.

I'd guess those predictions you made last January may prove rather accurate.  may be a good wknd for other outdoor activities.

Looks like they were spot on. From NWAC:

This upcoming hot weather is expected to cause a widespread
spring avalanche cycle in most areas starting Thursday. The
relatively prolonged hot weather should melt and weaken
significant near surface snow and allow melt water to possibly
percolate to deeper older weak layers. This is most likely on
slopes facing the sun but should also be likely on any steep
aspects. Deep avalanches are possible. Some slides may release
to or near the ground, involving the entire winter’s snowpack.
The expected large wet snow avalanches may travel very fast
and run long distances, possibly to lower elevations where
little or no snow cover may remain or to valley floors.

We do not recommend back country travel near any avalanche
terrain Thursday and Friday and possibly through the weekend.
Initially small wet loose avalanches may trigger large and
deeper wet loose or wet slab avalanches. Back country
travelers should also avoid slopes below cornices or gullies
and flat areas below avalanche run out zones. A lack of
refreezing at night may contribute to the avalanche cycle.
Remember that boot or ski penetration of more than a few
inches can indicate snow is becoming significantly unstable on
steep slopes.

Glad the NW Avalanche Center put out a special bulletin, I expected they would.

The snowpack is not nearly as well consolidated as usual for this time of year and now comes record or near record high temperatures, so I would think looking at this before it happens, it should be pretty much a worse case scenario. In my recollection I don't recall such a dramatic shift from persistent cool early and mid-spring conditions to such dramatic and intense heating. Whether or not and how frequently the slides go to the deeper snowpack (February - at least, remember it didn't snow much for 5-6 weeks so the pack consolidated then) is anybody's guess, but some of the slides should involve much of spring's snows. The slides could be slabs, but even wet loose slides in this situation are a major concern because of the probability of a lot of entrainment. The other really bad layer is the early December layer.

East of the crest the snowpack is weaker, in some areas down to the ground. I was surprised in March to find heavily faceted snow at the base of Blewett Pass's snowpack. The faceting was much more pronounced than normal, despite more than average winter cloudiness. So, in areas east of the crest without deep snowpack, it wouldn't be surprising to see those slides go to the ground.

Current models now show a pretty good drop in the freezing level Tuesday but possibly warmer weather again late next week. It will take more than a day or so of cooler weather to help stabilize things after this dramatic ramp up in temperatures.

...this is second hand info but i figured i'd post it anyways.... a friend of mine who was just up high on Rainier over the past few days trying to get in a climb described conditions on the upper mountain as 'waist deep wallowing' and said the glaciers haven't been refreezing at night.

I really wanted to ski Rainier this weekend...but gonna opt for some quality time on my surfboard instead.

Like Gary said this is the worst (best) case scenario for a spring cycle. Double usual snowpack, no significant warm ups so far this year, and now Mother Nature is going to apply the most heat possible to the snowpack. So layers or no layers its going to go. Look out below! I hope we avoid fatalities.

holy crapballs at blackcomb!

www.tetongravity.com/forums/showthread.php?t=123577

holy crapballs at blackcomb!

www.tetongravity.com/forums/showthread.php?t=123577

It sure shows that the cycle was a widespread one and worse in areas that were colder in early December. It's noteworthy that many of the slides broke out in shallower areas - a sign of faceted snow or depth hoar.

A couple of the Whistler slides Lee Lau posted were amazing for the width of propagation, which speaks to the weakness of the basal layer. One of them even crossed two major ridgelines!

With poor freezes due to lack of clear skies and a rebound in the freezing level on the weekend some more stuff may well rip out given the "success" avalanches had last weekend.