Buried weak layer of surface hoar sitting just above ice crust bed surface with increasing wind slab build up on all exposed and unsheltered aspects will create considerable avalanche conditions in the Selkirk and Cabinet ranges.
Buried surface hoar more dominant throughout all of the forecast zone. It can be anywhere from a foot deep to multiple feet depending on wind transport. Keep in mind that it has been buried for over a week and that it may be stubborn to go but if it does it will likely propogate quickly over a large area.
With the weeks periodic wind events that started last Saturday affecting the storm snow that fell atop the ice crust expect expect wind slabs all over. Current and recent winds have been howling out of the NE which is likely to slab up most areas that are unsheltered. It may or may not take much to penetrate down through these slabs to the weak layer depending on how thick the slab is at the point of triggering. Yesterday in the Selkirks we observed an avalanche that was triggered by snowmobile from the bottom of a slope in a low slope angle area that propogated up and across a larger steeper slope with a convex rollover mid slope. With the slabbing potential, these types of avalanches will be more likely to be larger in size and potentially take out bowls over the adjacent ridges.
Yesterday Lance and I traveled into the Selkirks to observe a recently triggered avalanche by a snowmobile on 2/9. If you look at the photos you can see the circle on the lower left where the trigger was initiated on lower angle terrain. The avalanche propogated up above on the near ridge and all the way up and across the small basin. There were some steep convex rollovers that were just enough to make things happen here. It was wind loaded on the left flank about 3 feet deep and on the right 1 foot deep. The buried surface hoar on the ice crust with a cohesive wind slab is what contributed to this avalanche. In the extreme terrain on windloaded NE aspects we saw evidence of multiple natural slides, however there were many similar slopes that have not yet slid. The weak surface hoar layer will likely be there for a while and although it may get more stubborn to trigger it is going to be a hazard for the foreseeable future.
You can see the red dot areas in the photo where there are terrain traps where the snow accumulation is about 15 deep in those areas. When in these areas below larger steeper terrain it is a good time to study the alpha angle and abide by the rule of 18....bottom line is you take the angle degree from where you are on flat terrain and to the top of the slope where a crown would likely occur and if you are 18 or less than you can be fairly confident that you will be clear of even the biggest slide from the slope in question.
