Increasing temperatures and the potential for rain on snow will increase the potential for triggering wind slabs created during the last week.   The latest wind event began on 12/21, and was able to trigger numerous natural wind slabs.  In many places these were older/ deeper windslabs that were failing on facets created in November.  

 New wind slabs could be reactive up to 1 foot in depth, or could overload deeper persistent wind slabs creating much deeper and more dangerous hard slab avalanches.  Slopes may fail once a person has travelled well out onto the slab.  Look for signs of windslab such as pillowed smooth snow surfaces, areas that have a hollow drum-like feel and shooting cracks.  Use caution, this is not our typical Thompson Pass snowpack, expect instability to linger longer after weather events than what is typical.

Temperatures will be increasing through the day as warm air overrides the cold air that is currently in place.  This may cause temperatures to go above the freezing mark in our high elevation start zones and create our first rain on snow event since October.  There will be the possibility for freezing rain during the day 12/26.  There is not a lot of precipitation forecasted for our area, although our snowpack has repeatedly showed us that even small changes in weather can rapidly increase the chances for avalanches to occur.  Expect for human triggered avalanches to become likely and natural avalanches possible during this change in weather.

A prolonged period of cold and dry weather beginning in November has created very weak faceted snow that is now buried in our snowpack.  The depth of where this layer exists in our snowpack is highly variable due to wind re-distribution.  These November facets can be found anywhere from at the surface in areas that have received heavy wind scouring to 3 feet deep in areas with thick wind deposits.  In areas more protected from the wind this number lies somewhere in between.

We have not had a major precipitation event in 3 weeks and temperatures have remained cold.  This has promoted faceting to continue in our snowpack.  Even with our fairly benign weather regime, minor changes in weather have resulted in natural avalanche activity.  This demonstrates our snowpacks’ inability to have stress applied without becoming reactive.  Stress can be applied in various ways including loading from wind, new snow, cornice fall or the additional weight of a person or snowmachine.  We have not seen precipitation or skiers/snowmachines testing slopes lately.  We have seen our fair share of loading from wind and the result has been natural avalanche cycles.

Persistent slab avalanches will not always give the typical signs of instability like shooting cracks or collapsing, and may fail after many tracks have been laid down.  Using safe protocols becomes even more important during this type of setup.  Some of these include only exposing one person at a time to an avalanche prone slope, have an escape route should a slope fail and maintain good communication with your group.

Photo of developed facets found on Girls Mtn at 3000′ SE aspect (2mm grid).   These were found 1 foot beneath the surface.  This layer of facets has been found at varying depths ranging from at the surface to 3+ feet deep.