A Special Avalanche Warning has been issued for this weekend. Now is an important time to exercise restraint and stick to low angle terrain.
Confidence
Poor - Due to the number of field observations
Weather Forecast
An Arctic high pressure system dominates the forecast for the next few days. Clear, cold, and dry conditions are expected until at least Thursday.Sunday: Sunny, treeline temperature around -20, light NW alpine wind Monday: A mix of sun and cloud, treeline temperature around -15, light W alpine wind Tuesday: Mostly sunny, treeline temperature around -15, moderate NW 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. Observations in the S. Columbia region are still very limited but it is expected that similar avalanche activity is occurring throughout the region.
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. 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.