Southeast Mountains

Clear evidence of dangerous avalanche conditions continues to unfold in the Southeast Mountains.  Yesterday, a group remotely triggered a large persistent slab avalanche that snapped trees.   Patience and conservative terrain selection are your best weapons for combatting the persistent slab dragon.    Although natural avalanches are unlikely today,  human triggering a persistent slab is still easy to do on slopes steeper than 35 degrees that face west through north through east, especially where seasonal winds have drifted snow into thicker drifts.  You can remotely trigger slides like this from adjacent to or below the start zone.  Collapses and shooting cracks are clear signs of danger.  

Observations suggest that, at least in the deepest parts of the Northwest Mountains, the snowpack continues to quiet down, trending towards better stability.   Don't let your guard down, even in areas where the danger is MODERATE. We are still getting reports of collapsing snow on specific terrain features, from the Anthracites  to Coney's.   Dangerous avalanche activity continues to be triggered in the Southeast Mountains, where the snowpack has been the most reactive on weaker layers in the past few days, and thus, a higher danger rating.   Skiers above West Brush Creek remotely triggered a large persistent slab avalanche yesterday that snapped small trees and put 8 feet of debris in the runout.    This avalanche was on an easterly facing, wind drifted slopes, the type of terrain that is most worrisome.  

Apart from the zonal differences that we've highlighted with the danger ratings, what types of terrain are you most likely to find trouble today?  This diagram shows the distribution of D2 or larger avalanches reported since our weak layers were buried on December 10th - a total of 165 slides large enough to bury you.  Each number on the diagram is a tally of avalanches for a given aspect and elevation wedge.  There are some terrain biases that influence the graphic (such as a lack of west and northwest facing paths below treeline), but it serves as a good approximation for where persistent slabs have been most active in the past month.  Our distribution rose for the persistent slab problem is forecaster crafted based on avalanche activity along with snowpack structure observations and tracking changes in the structure from wind, sun, etc.   In the Northwest Mountains, you are most likely to find instabilities in the parts of the forecast area that have received the least amount of snow this season, or in terrain where snow depths are more variable due to winds.  In the Southeast Mountains, the snowpack is thinner and slabs are starting to decay away below treeline.  You are most likely to find trouble in wind loaded terrain or on sheltered below treeline slopes holding enough of a slab (about a foot or more) to still be reactive over the large-grained depth hoar and facets just above the ground.   The safest options, apart from low angle terrain, are on the southern quadrant of the rose or in terrain that has previously avalanched.  There are some exceptions to this, especially on southeast aspects.  We've seen a few remotely or naturally triggered persistent slabs at all elevations on southeast aspects, in terrain where basal crusts are thinner and more collapsible.  You can find these thinner crusts at higher elevations or where trees cast shadows on pockets of the slope, making the snowpack behave more like an easterly aspect.