Weak Layers
As we approach the halfway point of February, we are yet again facing an onslaught of warmer weather as a ridge of high pressure moves into BC and establishes a pattern of dry weather and warm air aloft, creating quite a strong temperature inversion in many areas. The first half of February produced a series of storms that buried a variety of persistent weak layers under 50-100 cm of snow. These weak layers formed during our last period of dry weather at the end of January and have been a recurring problem these last couple of weeks with multiple skier accidentals across BC.
Skier reactivity on these layers had started to subside as time passed but with the forecasted warm weather and solar input, we should expect things to become more reactive again as the snow above the weak layer settles into an even more cohesive slab. The possibility of cornice failures and subsequent avalanches triggered by these cornices would be very large if they fail on the persistent weak layers. It will be important to practice conservative terrain choices for the next little while as the nice weather will try and lure us out into bigger terrain and untouched slopes. Be mindful of your overhead hazards and any steeper, unsupported terrain especially around treeline. These weak layers are difficult to pinpoint and will be your classic low probability/high consequence avalanche problem.
If you need any more information about your specific area, make sure to visit Avalanche Canada’s website and also make sure you review the Special Public Avalanche Warning they posted last weekend. Results of testing we did on Sunday, Feb 13th clearly reflect the reasoning behind Avalanche Canada’s SPAW. Here are the details, N. aspect, 2040m produced a CTM(14) and a ECTP down 38cms on surface hoar to 10mms. This is a pretty dramatic result and worth noting.