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Advisory—as of Wednesday, Jan. 13:
At the time of writing this advisory the Sea to Sky region is getting hammered by a wet and warm coastal storm. Usually, these stormy periods make avalanche forecasting easy as the warm, wet, and windy weather results in widespread direct-action avalanches and HIGH avalanche danger. Most folks tend to hunker down and wait out the storm, staying inbounds, letting the snowpack do its thing, and then heading out once things cool off, dry out, and the hazard decreases. Easy right?
Forecasting is not so easy this time—writing this mid-storm while trying to predict how the conditions will play out by the weekend with a complex snowpack and a persistent slab problem. As you can probably tell, there’s definitely some uncertainty.
The snowpack for the Sea to Sky region is currently complex, with multiple avalanche problems from direct-action storm and wind slabs. Most concerning is a persistent slab problem. The upper 200 centimetres of the snowpack hosts numerous buried weak layers, including a surface hoar/crust interface down 150 to 200 cm that was easily reactive to rider triggers last weekend. The hotspot was the Whistler backcountry.
A persistent slab avalanche problem is one that tends to catch backcountry recreationists by surprise, as the hazard is not obvious. The danger rating might only be moderate (or considerable), the likelihood of triggering an avalanche could be low, and there may be no signs of instability. But, the consequences of an avalanche are very high due to the potential size of any slide you trigger. The large size 3 avalanche that was triggered by the weight of a person last Saturday, Jan 9, on Cowboy Ridge is a prime example of this low-probability, high-consequence situation.
Much uncertainty exists with this persistent slab problem. The best-case scenario is that the storm from earlier this week was so warm and wet that the upper snowpack reached its critical load and flushed out this reactive slab. The worst-case scenario is that the storm adds to the load on this persistent weak layer and it continues to lurk, waiting for just the right trigger before unleashing on an unsuspecting individual.
Our advice for backcountry users heading into the weekend is to make sure that you check the forecasts at avalanche.ca for the most up-to-date information. Select conservative terrain that matches the avalanche hazard and avalanche problems, and don’t let the periods of sunshine and fresh powder lure you into big terrain without knowing what’s lurking in the snowpack beneath your feet. The snowpack will require some time to settle and stabilize, and when you see that persistent slab problem, it’s a good idea to dial it back, especially during times of uncertainty.
