50 to 80 cm of new snow from the past week rests on a variety weak layers. It is best to adopt a conservative approach to terrain selection as the snowpack adjusts the load.
There is lots of snow available for recent moderate to strong northwesterly winds to transport into alpine and treeline lee terrain.
The last storm pushed the persistent slab problem over the tipping point resulting in very large avalanches Saturday & Sunday. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.
TUESDAY NIGHT: Broken cloud cover, moderate northwest wind, alpine temperature near -12 C.
WEDNESDAY: Scattered cloud cover, light to moderate west wind, alpine temperature near -6 C.
THURSDAY: Mainly sunny, light southerly wind, alpine temperature near -2 C with potential for a light alpine temperature inversion.
FRIDAY: Mix of sun and cloud, light southwest wind, alpine temperature near -5 C.
Over the weekend a natural avalanche cycle took place with avalanches averaging size 1.5 to 2.5, but there were a few size 3 and even size 3.5's in the mix too. Many of the larger avalanches likely ran on persistent weak layers.
60 to 100 cm of storm snow has fallen over the last week. Underneath this storm snow there is a sandwich of weak layers which are widespread throughout the region.
Just under the new snow, down about one meter below the surface is the mid December surface hoar. This layer has been failing naturally and has been quite sensitive to human triggering throughout the storm cycle. Large avalanches have been running on this interface connecting big terrain features.
Below that lies the early December persistent weak layer, it's about 80 to 140 cm below the surface. This weak layer is a mixed bag that often presents as surface hoar and facets sitting on top of a stout supportive crust. This is a nasty weak layer, when avalanches fail on it, they have been large and destructive. Smaller avalanches in motion can step down to this one too. This weak layer is going to haunt us for the foreseeable future.
