Northwest Mountains

The hits keep coming, and our meager and weak snowpack will be struggling today.  Significant wind transport yesterday puts leeward terrain in the bullseye for dangerous conditions: slabs can break in the newly drifted snow, or step down into older weak layers producing a much larger avalanche.  Choose conservative terrain near and above treeline.   At lower elevations, slabs are less common, and old faceted rain crusts have done a better job of supporting recent snow loads.  Carefully assess the snowpack and watch for obvious signs of instability, especially as you climb above 10,500'. 

Yesterday's storm finished with a similar SWE load as Friday's storm and notable cycle in the Ruby Range: up to 1.2" in the Northwest Mountains and up to .7" in the Southeast Mountains.  This storm brought stronger, more productive wind speeds (see Irwin's observation). Alpine stations were averaging an ideal 20 to 30 mph from SW to W, loading onto our most worrisome aspects.  If visibility allows, it will be interesting to see how our snowpack responded.  We expect many wind-loaded slopes to be near their human-triggering tipping point, with the potential for the largest persistent slab avalanches in the Ruby Range (mostly D2-D2.5, isolated D3 potential).   We've had very few field visits to the higher terrain east of town, and our uncertainty there is greater.  We know the snowpack was exceptionally shallow and weak going into the start of our loading period on Christmas, and stress over those layers is gradually building, especially on slopes favored by yesterday's productive wind drifting.  SWE totals on our December dryspell layer (the Christmas facets and crust/facet layers) now range from 3.8" (Schofield) to 3.9" (Irwin) in the Northwest Mountains, and 1.5" (Butte), 1.9" (Upper Taylor), ~2.2" (Gothic), and 2.8" (Castle Peak) in/near the Southeast Mountains.  Bottom line: as you gain elevation and as you move further from the middle of the CB donut hole, expect increasingly dangerous conditions.  

Below treeline has been remarkably quiet in the past few weeks, with only a few small avalanches reported below 10,800'.  With each loading event, our uncertainty about the faceted rain crust waking up increases.  The crust is thinnest and most collapsible as you gain elevation closer to treeline, and slabs are more developed the higher you go: that's where I expect the first surprises to occur.  If you are riding in steep, wind-sheltered terrain at lower elevations, stay alert for signs of instability and evaluate both slab size and terrain consequences.