Northwest Mountains

The snowpack is screaming "Danger!"  There have been dozens of large natural and human-triggered avalanches in the past two days.  We have multiple weak layers in our snowpack that have all come to life with the recent storm.  Expect sensitive conditions, remote triggering, and unusual avalanche behavior today.  Conservative terrain choices are essential.  The snowpack is less problematic on wind-sheltered southerly aspects, but still requires caution, especially as the snow surface gets moist and sluffy.

Good visibility yesterday allowed us to document the numerous large avalanches that ran during or in the wake of this weekend's storm.  So far we've documented 25 large avalanches, mostly in the Northwest Mountains (biased by our fieldwork locations yesterday), and a similar pattern of large avalanches occurred on the deeper Marble side of the Elks.   Most of these avalanches broke about 2 feet thick on the storm interface consisting of facets, surface hoar, or crusts (see video describing these layers from before the storm).  We also documented a handful of hard slabs that broke into older weak layers below our January slabs.  These were most commonly on shallower slopes (ex. Redwell 1, Redwell 2) or where sizeable slabs in the upper snowpack gained enough mass to pry out old hard slabs (ex. Axtell, Bellview).  This very large avalanche in the Raggeds is notable because it failed directly into old layers on an aspect where the snowpack is deep.  Take note of these avalanche patterns; there will be more to come with the midweek storm, and we could see a few more big ones go today from solar-triggered sluffs or if wind drifting occurs.  

Today, we are transitioning the storm slab problem into our newest generation of persistent slabs because the storm snow fell on persistent weak layers (surface hoar and facets), most commonly on west, north, and east aspects.  Slabs have already been exhibiting persistent slab-like behavior, with numerous remote triggers and avalanches breaking on lower-than-usual slope angles.  A word of caution because we don't deal with buried surface hoar issues as frequently here:  Surface hoar is a notoriously tricky weak layer known for releasing on lower slope angles (low 30's, and in rare cases, high 20's), with hit-or-miss feedback and signs of instabilities.   The recently buried facets and surface hoar issues will likely remain sensitive through the next few days and only get worse with the storm coming this week.   

Some options for lower risks.  1) Low-angle terrain or small, inconsequential terrain features.   2) Mid to low elevation southerly aspects:  persistent slab issues are less likely to be found where thick crusts are bridging old weak layers and destroyed our most recent ones. Carefully evaluate for exceptions and stay alert for lingering storm instabilities or wet loose avalanches today.   3) Low elevations in the Southeast Mountains.  Newly formed slabs over our latest weak layers haven't fully developed yet on most below-treeline slopes in the shallow zone: watch for exceptions near the zone boundaries or where you find more than a foot of recent snow, and evaluate for lingering threats from old weak layers near the ground.