Regions
Northwest Coastal.
Stormy conditions are elevating the avalanche danger to HIGH. Strong winds and heavy precipitation are developing new storm slabs, and deeply buried weak layers are still a concern for very large avalanches.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
15-20 cm of snow above about 700 metres overnight with winds becoming moderate westerly. 5-10 cm of snow above 500 metres during the day on Saturday with moderate westerly winds. Heavy precipitation, strong southerly winds and freezing levels rising up to 1500 metres on Sunday. Continued heavy precipitation, strong winds, and high freezing levels on Monday.
Avalanche Summary
No new avalanches reported. Suspect that a natural storm snow cycle occurred today in the alpine and at treeline with heavy loading from strong winds, new snow, and rain below 800 metres.
Snowpack Summary
New storm slabs developed on Friday due to strong southwest winds and heavy precipitation. Before the new storm, in the north of the region there was 20-30 cm of recent snow that had been transported into deep windslabs above loose facetted snow in sheltered areas, and stiff old wind effected surfaces in exposed terrain. In the south of the region we had reports of 10-20 cm of recent snow that was sitting on a new surface hoar layer that was buried on February 3rd. Wind slabs developed in the lee of southeast winds on Wednesday, and more widespread storm slabs developed on Thursday. The January 9th surface hoar/facet layer is down 70-150 cm in most places, and remains a concern on all aspects and elevations, especially with heavy and/or thin-spot triggers. Around the same depth you may also find a surface hoar/facet interface from around New Years. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem. A conservative approach to mountain travel is still required.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.