Today it is still possible to trigger an avalanche on weak layers of snow in the upper 2’ of the snowpack. These layers formed during dry spells in late January and early February, have recently produced avalanches (examples here and here) and continue to show poor results in stability tests. In some areas we are dealing with buried surface hoar, others are a combination of decomposing stellars and near-surface facets, and many places have both. These layers are particularly concerning where buried surface hoar sits on top of a rain crust at elevations up to 1200-2000′. The key to staying out of trouble today will be avoiding steep slopes where those weak layers are capped by stiff snow near the surface. A few inches of snow from last night will not increase the avalanche danger, but it may make it more difficult to identify slopes that were previously wind-loaded. You can still look for slabs as you travel, and it can be as easy as hopping off your machine and poking into the snow, or stepping off the skin track to probe around as you approach your objective.
Persistent weak layers will sometimes– not always– give clear warning signs prior to avalanching. If you notice shooting cracks or collapsing, these are sure signs that the snowpack is capable of avalanching and it is time to stick to low-angle terrain. These persistent weak layers become more difficult to anticipate in the absence of these warning signs. When we are dealing with uncertainty in the strength of the snowpack, and in the reactivity of persistent weak layers, it is important to increase our margin of safety by minimizing exposure to consequential terrain.
We are expecting to see more snow tonight and into tomorrow. Snow and winds are not expected to pick up until later tonight, but the active weather may increase avalanche danger. Pay attention to changing conditions later in the day today, keep your fingers crossed for snow, and stay tuned for more!
Sluffs: Be aware of dry loose avalanches on slopes that have been sheltered from the wind. While it is unlikely they would be big enough to bury a person, they can become dangerous if they carry you down steep slopes and into terrain traps.
Cornices: Large cornices have been peeling away from ridgelines, opening up large cracks. If you are traveling along ridges be sure to give them plenty of space, and minimize the amount of time you spend traveling below them.
Looking down at the natural avalanche on Eddies (first observed on 02.12). The avalanche failed on a layer of buried surface hoar and near-surface facets about 12″ deep, and quickly stepped down to a deeper layer of buried surface hoar. 02.15.2021
Two layers of buried surface hoar, plus a fresh layer on the surface which just got buried this morning. Eddies. 02.15.2021
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