A deeply buried weak layer means human-triggered avalanches will persist. Conservative decision making remains critical.
Confidence
Poor - Due to the number of field observations
Weather Forecast
A weak disturbance will bring increased cloud and possibly light flurries for Monday. Clear, dry conditions should return for Tuesday and Wednesday.Monday: A mix of sun and cloud, light flurries 0-2cm, treeline temperature around -18, light-moderate W alpine wind.Tuesday: Mostly sunny, treeline temperature around -15, moderate-strong NW alpine wind.Wednesday: Sunny, treeline temperature around -12, light variable alpine wind.
Avalanche Summary
On Thursday and Friday, widespread natural avalanches up to size 3.5 were reported in the Rogers Pass area. Avalanche control on Friday afternoon produced numerous results up to size 3.5. A natural size 3 avalanche was reported in the same area on Saturday morning. In the Monashees, natural size 2 and 2.5 avalanches were reported on Saturday.
Snowpack Summary
The recent storm produced a slab up to 1m thick which sits on the mid-November weak layer (facets, surface hoar, and/or a sun crust on steep southerly slopes). 20-30cm below this layer is a thick rain crust with weak facets on top. Both of these deep layers are expected to persist and continue to produce avalanches. Snowpack tests on Sunday in Rogers Pass suggest the layers can still be human triggered, and if triggered, are capable of producing wide propagations and large avalanches. On Thursday, high elevation rain produced a new crust. In the north of the region this rain crust exists up to around 1500m whereas in the south it is up to 2000m or higher. As temperatures dropped, 10-20cm of new snow fell on top of this new crust. Recent strong and variable winds have created wind slabs in exposed terrain and resulted in variable snow distribution in the alpine.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.