Watch for fresh storm slabs building throughout the day. New snow is likely to be most reactive in wind loaded terrain features. Be prepared to dial back your terrain choices if you encounter signs of instability such as shooting cracks or recent avalanches.
New snow and wind are forming fresh, reactive storm slabs. Storm slabs are most likely to be reactive in wind loaded features and where the new snow sits over surface hoar or a crust.
The early December crust can be found down 100-200 cm below the surface, with weak, sugary crystals (facets) on top of it. The likelihood of triggering an avalanche on this layer is decreasing but still remains a concern for avalanches stepping down. We are now in a low probability/high consequence scenario with this layer.
Sunday night: Snowfall 5-15 cm. Moderate SW wind. Freezing levels around 800 m.
Monday: Snowfall 5-15 cm. Moderate SW wind. Treeline high around -1 °C. Freezing levels rising to 1400 m.
Tuesday: Mainly sunny. Light variable wind. Treeline high around -6 °C. Freezing level valley bottom.
Wednesday: Mainly sunny. Light variable wind. Treeline high around -8 °C. Freezing level valley bottom.
On Saturday, wind slabs on E-NE aspects in the alpine were reactive naturally and to ski cuts size 1-1.5. Natural and explosive triggered loose wet and wet slab avalanches size 2-2.5 were reported below 1000 m.
A warm storm on Wednesday and Thursday last week triggered a widespread natural avalanche cycle up to size 3.5 (very large) at upper elevations. At lower elevations, loose wet activity was widely observed. By Friday, natural storm slab activity had largely tapered in size and number, but explosive control work continued to produce results up to size 2.
As of Saturday, observations continue to roll in from throughout the region of several persistent slab avalanches on the early December layer, suspected to have run during the warm storm Wednesday/Thursday. These avalanches are generally around treeline elevation (1700-1900m), size 2.5-3.5 (very large), 100-150 cm deep and on a variety of aspects in both the Selkirks and Monashees.
New snow falls over 25-50 cm of well settled snow from the previous storm, a possible layer of surface hoar crystals in sheltered areas, and/or a thin breakable crust which was observed as high as 1800 m in the Selkirks and into the alpine in the Monashees.
A couple of layers of weak facets and/or surface hoar that were buried earlier in January now sit 25-50 cm and 50-90 cm deep.
The early December crust/facet interface is now typically down 80-140 cm, but as deep as 200 cm in wind loaded terrain. It consists of faceted grains above a decomposing crust formed by the Atmospheric River rain event at the end of November. There has been avalanche activity on this layer as recently as recently as Friday in the region. Heavy triggers like natural cornice falls and storm slab avalanches may still have potential to step down to this layer resulting in very large avalanches.
