Human-triggered avalanches are likely today in areas where a slab overlies weak faceted snow. You could trigger a large avalanche on terrain features >30 degrees that have received recent wind loading. To avoid avalanche hazard, stick to slopes <30 degrees and avoid traveling below avalanche runouts.
This forecast is sponsored by Anthony Lakes Mountain Resort.
Winds in the low teens combined with abundant snow for transport could build reactive windslabs on exposed features near treeline and above. If you see signs of wind slab activity such as dune-like formations, textured snow surface and shooting cracks avoid slopes >30 degrees. Adding a slab along with a trigger to our poor snowpack structure could trigger an avalanche larger than anticipated.
January's long high pressure weakened the upper snowpack and created several layers of incohesive facets that are now buried 1-2 feet thick across the forecast area. On southern aspects these weak grains exist beneath sun crusts. While evidence of this instability may be sparse, the poor structure of the snowpack is not to be trusted. Currently, February's storm snow is slowly settling into a cohesive slab, and reactivity will increase in areas where wind slabs sit atop this poor structure. Patience will be required, as the only way to truly avoid avalanche risk is to avoid avalanche terrain and recreate on slopes under 30 degrees.
This observation from the Southern Wallowas yesterday highlights the potential complexity of our snowpack - a natural avalanche roughly 50m wide suspected to have failed in the previous 24hrs, likely in an area where winds had deposited enough snow to create a strong (and heavy) slab above weak structure. Forecasters visited the Elkhorns yesterday and received propagation in three separate ECT tests - read the full observation here.
What to do: Persistent slab problems are notoriously difficult to manage due to a lack of feedback. You may not observe any signs of instability. Natural persistent slab avalanches are rare after the initial loading period. Slopes capable of avalanching may even already have tracks on them. Until the snowpack structure improves the only way to eliminate the risk of avalanches is to avoid terrain steeper than 30 degrees, especially with the potential for overlapping avalanche problems.
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