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.