early season avy danger?

[marylou]

I was talking last night with someone about doing some BC skiing next week. I expressed some trepidation due to all the weather we're having, and he said "there's virtually no avalanche damage this early in the season, due to there being so many terrain anchors in a low snowpack."

 

Makes sense, but I had not heard that before. Can someone second that opinion? I'm still a total snowpack n00b. Thx.

[colt45]

That sounds like a pretty big generalization. As long as there is enough snow to create a homogenous surface (ie enough snow for skiing to actually be enjoyable), it should be possible to form layers in the snowpack which could fail. Moreover a shallow snowpack is prone to faceting.

[dbconlin]

colt 45 has a good point regarding shallow snowpacks being prone to faceting. Of course it depends on the temperature gradient, i.e. the difference in temperature between the ground beneath the snow and the air above it. In a shallow snowpack, the ground can be relatively warm while the air temp is very cold, creating a steep gradient. This results in faceting of the crystals, forming a hoar layer, which is basically like the ball-bearings upon which a consolidated layer above may slide. Of course to have a slab avalanche, the above layer must be consolidated enough to cohere. Additionally this type of temperature gradient is less likely to occur in Washington, where the air generally isn't that cold. But it can be. So it depends on current conditions, features of the snowpack that may be quite different between aspects and locality, etc. Generally speaking, there isn't very significant avy danger in WA this time of year, but that isn't an absolute rule and it would be wise to evaluate conditions in the field as you go and remain cautious, especially in light of the substantial and continuing precip that has accumulated and is expected.

 

Another caveat is that while terrain features may 'anchor' the snowpack, in other cases they can serve as a weakness in a consolidated snow layer, from which a failure might originate. Therefore the presence of large rocks and trees that extend through the snowpack and are still visible should actually be a warning sign.

 

Finally, avalanches are known to slide all the way to the ground surface, where the ground itself is the sliding surface, rather than a smooth consolidated snow surface as is often assumed. In this case a shallow snowpack can still slide, even without the formation of multiple layers over time.

 

Disclaimer: most of my avy training has occured in Colorado where the snowpack is very different from Wa.

[chris]

Snbowpack has bonded well to the surface in every report I've heard, which fits a cooling trend. Since the snow has fallen very consistently in the past 72 hours, I wouldn't expect distinct layers to have formed.

HOWEVER: I will be looking for windpacking after last nights event, and watching the temperature tomorrow.

In my injured state, I'm not supposed to go skiing or lift more than 10 lbs. But I plan on digging a pit near Mt. Baker on Friday, weather permitting. Of course, skis may be the most expedient method to travel to the pit site...

[PaulB]

These reports on TTips from around the Mt. Baker ski area indicate that slides were easily triggered this weekend.

[Weekend_Climberz]

I would think the danger on permanent snowfields is going to be much higher than lower down. Just watch the terrain and jump test. Jump, Jump, Rip, baby.

[chris]

These reports on TTips from around the Mt. Baker ski area indicate that slides were easily triggered this weekend.

 

Wow! Not what I had heard - thanks for the link Paul.

Sounds like ski cutting is mandatory until we're confident that this 12-18 inches of heavier snow has bonded.

[Farrgo]

I remember reading a report about a pretty scary slide in early season conditions on a summer ice field. I'll link it if I can remember where it was. Ski cutting is an advanced technique. While I know Chris is a guide and spends more days in the field per year than I have in my life, I would be leary of ski cutting. You really need to know what your doing to make sure your cut is in the right spot or you might end up trigging the slide with you in it. Take an avy course, or two, or three. The more knowledge you have the more aware of dangers your going to be. I would tend to agree with your friend if your talking about not a lot of snow with many obstacles exposed. If your talking about new snow on top of old snow, its a different story. I'm not an expert but I've kind of taken to heart, "if you can ski it, it can slide." So, don't think just because its early season, its game on, you still need to be aware.