The Pineapple Express and Extreme Avalanche danger
A Pineapple Express is approaching the coast, and conditions have changed yet again. Everyone should take a moment to appreciate the significance of Extreme Avalanche hazard on the south coast. Take a moment to understand what extreme means:
Likelihood of Avalanches: Natural and human triggered avalanches certain.
The way I like to look at this is as follows: when I’m on a slope I think to myself “could I trigger an avalanche if I wanted to, and how would I go about it”. This puts me in the mind of looking for the sweet spot, or trigger, which I can then avoid. I know it sounds strange, but this technique of looking for the instability gives you guidance to where the stable areas might be. During a period of extreme hazard, it is very very easy to find and trigger avalanches, and natural avalanches are also happening.
Avalanche Size and Distribution: Large to very large avalanches in many areas.
It’s not enough to know the likelihood, you need to know the size, and the distribution. This means larger than normal, and on more slopes. One of the things you hear on the news from uneducated backcountry enthusiasts after an avalanche is something like “I’ve been sledding/skiing/boarding/hiking there for 20 years and it’s never slid before” – this is the important thing to remember, it’s not just the terrain, it’s the conditions and weather history. During this period, those areas you’ve never seen slide before are ready for their 15 minutes of fame.
Travel Advice: Avoid all avalanche terrain.
Just good advice, but what is avalanche terrain? Basically, if you can have fun skiing it (20 degrees plus), it’s avalanche terrain, and could. under the right circumstances, slide. Not only that, given the above advice on likelihood, size and distribution there is the possibility of being hit by a natural – meaning that even if you’re not on the start zone, you could be hit by a natural coming at you from above.
This is a rare event in a region typically known for very deep, stable snowpacks.
Analyzing the latest bulletin, we can see a specific reference to a deep slab, and a rain crust from November buried 1 to 2 meters deep. 30-40cm is snow is forecast to fall, but freezing levels are at 2300m, which means rain and very heavy snow at lower elevations.
Rain and heavy snow add weight, but no strength to the snowpack,at least initially (unless temperatures drop, and it freezes). This means a greater load with less strength, on top of the large dumps of snow from earlier this week. Hence, the possibility of triggering the deeper, buried instability.
Reading the Marine Synopsys doesn’t inform us of any other weather systems to worry about, and the weather warnings only speak of one system generating rain.
Perhaps a good weekend to go indoor rock climbing.