Northwest Mountains

An Avalanche Warning remains in effect through today.  Here comes the wind! The threat of large natural avalanches is increasing, especially in leeward terrain.  In sheltered terrain, avalanches breaking about two feet deep are easy to trigger on west, north, or east aspects.  There have been dozens of remotely triggered avalanches in the past few days: avoid crossing below steep slopes threatened by overhead hazards on those problematic aspects.  You can safely enjoy the powder on slope angles consistently less than 30 degrees.  Wind-protected southerly aspects offer less risky riding options.   

Yesterday's lull in stormy weather allowed our forecast team to document over 70 natural avalanches that ran during the snowfall events from Friday through Sunday morning.  Paired with the 40 human-triggered avalanches (most of which were remote), our avalanche database paints a clear picture of where you are most likely to dance with the persistent slab devil today:  West, north, and east aspects and potentially a few southeast aspects above treeline, where slabs ranging from 1 to 2+ feet thick formed over the fragile weak layers of our December dry spell. The near and below treeline elevations were most active because those slopes held the weakest snow before the storm, whereas alpine slopes held a variable mix often featuring wind-hardened surfaces capping weaker snow.  Yesterday's observations are highlighted by several remarkable remote triggers, including multiple slides triggered from flat terrain 1000' to 2000' away from start zones.  The unusual remote triggering conditions right now mean you may need to re-evaluate your standard trade routes and up-tracks: you can trigger a dangerous avalanche above you while moving through low-angle terrain that seems benign.  With ongoing loading today, natural avalanches are also a serious concern and could become likely on windloaded slopes.  

Along with another half inch of snow water equivalent overnight, the big change today is the wind.  During the first few days of this storm cycle, winds have remained relatively tame.  That changed in a big way last night, with sustained strong winds blowing in the alpine and strong gusts mixing into our near treeline stations.  That pattern continues today.  The winds have about 3" to 7" of new snow to transport, and if they can peel back the dense, occasionally crusted snow that fell on Saturday night, they'll find an abundance of easily transportable snow from last week's snowfall.  Slopes where fresh wind loading overlaps with our active, persistent slab problem are prime suspects for more large natural activity.  We saw some large natural activity creeping into our shallow zone over the weekend (ex. Gothic, Little Lady Bowl, Climax). That pattern is expected to escalate with today's windloading, which is increasing the size of slabs and stress on leeward slopes.   Uncertainty remains for how our alpine slopes will behave. We decided to err on the side of HIGH danger above treeline given the most significant wind loading period of the week ongoing right now.  We may see less natural activity, but if the hard wind board capping basal facets reaches a breaking point, expect wide and dangerous avalanches.