Christmas Day! The trouble spots will be north and east aspects below ridgelines where recent winds have loaded in snow on last Mondays' rain crust. Isolated wind slab avalanches are possible in steep terrain at such locations. Persistent weak layers such as crust facet combos are still a problem as well. Human triggered avalanches are possible in steep, open terrain above 5,500' in elevation. On Saturday we are forecast to have a fresh 4-6" of snow on the ground, this may cause some sloughing and thin storm slab potential in steep terrain through the weekend.
Recent snowfall from last Tuesday is being pushed around by a southwest wind. Human triggered avalanches will be possible in steep, leeward terrain (north and easterly aspects). These slabs will be 12" or greater in depth, observations on Thursday showed these slabs to be fairly stubborn to human triggers and isolated below ridges and in steep gullies.
There are a variety of layers out there across the Kootenai area that are buried within the snowpack at varying depths. Most concerning are a number of crust/facet combos and new snow laying on top of the most recent crust layers. Stability tests are showing these layers to be propagating with moderate to hard force. Take-home message from my end is to assess steep slopes with suspicion, each one is guilty until proven innocent. They will be resistant to triggering but may go big when they fail. Take time to dig a pit and utilize low consequence test slopes before commiting to bigger terrain.
Here lies the nitty-gritty for the Christmas weekend. Rewind to Monday and you will remember a warm and rainy day, we found a stout rain crust that was about 6" thick up to 5,500' in elevation. Below this mark conditions were very firm and stable. The only concern below this mark lies mainly with the fresh crop of surface hoar that is growing under these cold and clear conditions, this may cause problems after our next heavy snowfall. Above this elevation the crust layer becomes breakable and slick. Observations in wind loaded locations were showing that the new snow was failing and propagating with moderate force in north and easterly aspects. Pit results on southerly terrain with thinner snow coverage reveal a combination of crusts, depth hoar and facets that may produce avalanches 2-3 feet deep. These layers will take a serious trigger to cause a problem and they just survived a pretty serious warm spell. So, I am calling them low-likelihood-high consequence kind of problem. Remember to look both ways before you pull out in front of the semi!
Getting to the weather forecast, Friday night into Saturday morning we should receive a modest shot of fresh snow. This new snow will likely cause some sloughing in steep terrain and some thin storm slabs. It may not be enough to bury you; but, worth paying attention to in steep and cliffy terrain.
Have a good Christmas, and hopefully, get some riding in as well.
