50 to 100 cm of recent storm snow rests on a smorgasbord of weak layers in our upper snowpack. It's time to scale the objectives way back and enjoy the simple pleasure of riding mellow well-supported treed features that are out of the wind and free of overhead hazard.
The last storm pushed the persistent slab problem over the tipping point resulting in very large avalanches Saturday & Sunday. Monday night's storm may add increased vigor to this problem. 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.
We could see as much as 20 cm of new snow Monday night into Tuesday with strong north wind. Watch for the formation of fresh sensitive slabs in the new snow.
An active storm cycle has produced 60 to 100 cm of storm snow 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. There are facets below the crust too. 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.
One last pulse tonight, and then it looks like we’re moving into a bit of a clearing trend this week.
MONDAY NIGHT: Freezing level near valley bottom, moderate to strong northerly wind, 5 to 15 cm of snow expected.
TUESDAY: Scattered cloud cover, freezing level at valley bottom, light northerly wind, no significant precipitation expected.
WEDNESDAY: A few clouds, freezing level at valley bottom, light southwest wind, no new snow expected.
THURSDAY: A few clouds, freezing level at valley bottom with potential for a light alpine temperature inversion, light southerly wind, no new snow expected.
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.
