Small storm slabs may be more reactive than expected; especially on slopes where it has been wind loaded and is sitting on a layer of fragile surface hoar. Recent cornice falls have produced large avalanches on deeply buried weak layers in this region.
Small storm slabs may be more reactive than expected; especially on slopes where it has been wind loaded and is sitting on a layer of fragile surface hoar.
Weak snow at the bottom of the snowpack continues to pose a deep persistent slab avalanche problem. The most recent activity has been focused around the Golden area, but steep, rocky, shallow terrain throughout the region should be treated with caution. Avoid big alpine slopes that are threatened by cornices overhead.
FRIDAY NIGHT: 3-5 cm. snow, strong southwest wind, alpine temperature -10 C, freezing level below valley bottom.
SATURDAY: 3-5 cm snow, moderate southwest wind, alpine temperature -5 C, freezing level 1100 m.
SUNDAY: 3-5 cm. snow, light to moderate southwest wind, alpine temperature -6 C, freezing level 800 m
MONDAY: Cloudy with possible flurries; 0-3 cm, light west wind, alpine temperature -5 C, freezing level 1000 m
There have been a few sporadic large avalanches over the past week. Most recently, a large (size 3) deep persistent slab avalanche was remotely triggered on Sunday just outside the forecast region near Mt. Seven. Photos in the Mountain Information Network report show this avalanche was initiated by a skier causing a whumpf on a ridge that released a small wind slab on an east-facing alpine slope which then stepped down to the facets at the bottom of the snowpack. Another size 2.5 deep persistent slab avalanche was observed on a southwest aspect in steep and rocky alpine terrain near Golden on Thursday (see MIN report). Additionally, a large snowmobile triggered avalanche was reported on a convex roll at treeline in Quartz Creek on Wednesday (see MIN report). These isolated, but large avalanches suggest that the Purcells region is currrently in a low probability, high consequence scenario that requires careful snowpack and terrain evaluation.
Clear and sunny skies have formed new surface hoar (size 3-10 mm.) on all but solar aspects where a new sun crust has been formed. This new interface will need to be carefully monitored as it gets buried. New snow falling on this layer will be more reactive than previous storms where the new snow did not fall on a persistent weak layer. At lower elevations (below 1600-2000 m) 20-40 cm of snow sits above a hard rain crust. The middle of the snowpack is strong, but the base of the snowpack contains basal facets that have resulted in sporadic, large deep persistent slab avalanches, especially in shallow rocky start zones.
