Northwest Coastal

New storm snow with strong winds will quickly increase the hazard on Tuesday.

Fair - Due to the number of field observations

A frontal system is expected to bring around 15-20mm of precipitation to the North Coast on Tuesday. Another 10-20mm is possible Tuesday night into Wednesday morning. Freezing levels on Tuesday are expected to be 800-1000m with strong-to-extreme winds from the SW in the alpine. On Wednesday, precipitation should taper off in the morning with freezing levels around 500m and winds easing to moderate NW in the alpine. Christmas day looks to be a mix of sun and clouds with freezing levels around 500m and moderate winds in the alpine.

Reports from Sunday of natural storm slab avalanches up to size 2.  These were typically 15-30cm thick slabs but the thickest reported was 70-80cm.  Typical start zone elevations were 1400-1500m. Explosive control also produced numerous storm slab avalanches with the same characteristics.  I expect we will see more natural storm slab activity on Tuesday.

A storm slab developed over the weekend that is about 50-70 cm thick at higher elevations. Strong Southwest winds have transported snow into windslabs that may be about 100 cm thick. Rain up to about 800-900 metres elevation may have resulted in loose wet avalanches where that rain fell on snow from earlier in the storm. Cornices are expected to be large and fragile due to new rapid growth. Deeper in the snowpack, weaknesses such as the mid-November crust-facet layer still exist. Avalanches at this interface have become unlikely, although the consequences of a release remain high. This layer may be more sensitive to triggering in steep, unsupported high alpine terrain, or in the far north of the region.