Use extra caution at treeline and below where persistent weak layers have been most reactive. Be aware that wind slabs could step down to these layers.
Natural avalanche activity has tapered off but human triggering of persistent slabs is still possible.
The last few days of variable winds have created wind slabs on all aspects at all elevations. As southerly winds increase the largest and most reactive wind slabs will be found on north aspects.
There are 2 persistent weak layers in the top meter of the snowpack. The first is a layer of facets formed during the period of arctic air and buried on December 22nd. Surface hoar could also be found at this interface in sheltered treeline features.
The second is a layer of facets and surface hoar from early December. This layer is buried as deep as 1 meter in some areas.
Both these layers are most concerning in sheltered features at treeline and below where surface hoar is more likely to be present.
On Friday, a skier accidental persistent slab avalanche was reported. The size 1.5 avalanche slid on a layer of depth hoar and facets close to the ground.
In the last few days several avalanches have been triggered at treeline and below on the layer of facets formed during the recent period of arctic air. Triggers have included vehicle remotes, skier remotes, naturals and explosives. These avalanches have generally ranged in size from 1 to 2.
5 -10 cm of new snow has buried a widespread layer of surface hoar in sheltered areas at treeline. Wind-affected surfaces are found in exposed areas at higher elevations and below treeline cross-loading will likely be found in all coastal inlets due to recent outflow. Below 1000 m a crust exists on or near the surface.
40 to 70cm overlies a weak layer formed during the previous period of arctic air. In the alpine this layer is generally facets but surface hoar could be found. At treeline it is more likely to find surface hoar at this interface in sheltered terrain.
A layer of surface hoar and facets from early December can be found down 70 to 100cm. recently this layer has not been reactive but still produces sudden results in snowpack tests.
Sunday Night
Mainly cloudy with isolated flurries, 1-5 cm accumulation. Light southerly ridgetop winds occasionally gusting 40km/h. A low of -4 at 1500m. Freezing levels 500m.
Monday
Cloudy with isolated flurries, 5-10 cm accumulation. Ridgetop winds southerly 30 to 50 km/h. A high of -5 at 1500m. Freezing levels 500m.
Tuesday
Mostly cloudy with sunny periods with isolated flurries, 1-5cm accumulation. Ridgetop winds southerly 20 km/h. A high of -7 at 1500m. Freezing levels 400m.
Wednesday
Mix of sun and cloud with isolated flurries, trace accumulation. Ridgetop winds southerly 20 km/h. A high of -7 at 1500m. Freezing levels valley bottom.
More details can be found in the Mountain Weather Forecast.
