The warm, wet, and windy storm continues to result in HIGH avalanche danger.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Very strong Southwest winds and heavy precipitation is expected overnight and ending Saturday morning as the second of three pulses of moisture moves into the region. The Northeast of the region may remain cooler due to the influence of the arctic air to the North. Freezing levels should be between 1500 metres in the northeast and 2200 metres in the Southwest. Cloudy with strong Southerly winds during the day on Saturday with light to moderate precipitation, and then heavy precipitation starting in the late afternoon or evening. Winds dropping to moderate on Sunday combined with light precipitation and freezing levels slowly dropping. A weak Low pressure system is expected to bring moderate to heavy snowfall on Monday combined with moderate Southerly winds.
Avalanche Summary
Widespread natural avalanche activity up to size 2.0 was reported from the Selkirks and Monashees where slab avalanches released within the storm snow on Thursday. Observations were limited due to poor visibility and travel conditions on Friday
Snowpack Summary
The new snow has settled into a reactive soft slab that may release on the buried end of January crust, or on a weakness within the storm snow that is 10-15 cm above the crust. Widespread windslabs at ridgetops may be easy to trigger where they are sitting on the crust that formed last week. The new storm slab is up to 60 cm thick and sits above a variety of old surfaces. The old surfaces include the crust that formed last week, a new layer of surface hoar that developed during the clear weather late last week, and in some places wind slabs that developed smooth hard surfaces. Deeper in the snowpack the mid-January surface hoar remains a concern. It can be found down 60-120 cm across the region, but in most places it is about one metre down. In some locations it has reportedly gained quite a bit of strength, but elsewhere it is still producing sudden collapse (popping) failures in snowpack tests. The mid-December surface hoar layer is now 80 to 140cm below the surface and has become unlikely to fail, the storm at the end of the week should be a good test to see if it will become active again.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.