Avalanche Forecast

A ridge of high pressure brings dry and sunny conditions for Thursday before the next storm system arrives Thursday night. 

Wednesday Overnight: Clouds clearing overnight, light variable wind, freezing level climbing as high as 1500 m. 

Thursday: Mainly sunny with increasing cloud in the late afternoon, light variable wind becoming moderate S in the afternoon, freezing level as high as 1800 m with an inversion. 

Friday: Snowfall 15-30 cm, strong S wind, freezing level around 1300 m. 

Friday overnight and Saturday: Snowfall 20-30 cm, strong SW wind, freezing level around 1000 m. 

On Tuesday, the natural cycle had tapered off but a few natural wind slabs were still being observed throughout the region. Skiers and explosives were triggering touchy storm slab avalanches on Tuesday mainly up to size 2. This MIN report describes a natural and a skier triggered avalanche west of Terrace. At lower elevations, natural wet slabs and loose wet avalanches have been widespread. 

On Sunday and Monday, a natural avalanche cycle occurred in the north of the region where 50-80+ cm of storm snow had accumulated. These were primarily storm slab avalanches up to size 4 which were most reactive in wind loaded terrain. In the south of the region, a variety of natural avalanche activity was reported but it doesn't seem to be as widespread as in the north and the avalanche sizes were generally smaller. 

On Monday in the far south of the region, explosives triggered a deep persistent avalanche which failed on basal facets near the ground. While this appears to be an isolated event, it could be an indicator that deeper weaknesses in the snowpack could be waking up with the warming temperatures. 

Mild temperatures are causing the 40-80 cm of recent storm snow to settle rapidly and slabs are expected to remain reactive, especially in wind loaded terrain. Below the recent storm snow is a highly variable snow surface which includes heavily wind-affected surfaces (scouring, old wind slabs, sastrugi, etc.) from last week's outflow winds, widespread faceting from the prolonged cold temperatures, and/or small surface hoar in sheltered terrain. This weak interface and a hard bed surface may increase the reactivity of the storm slabs.

The early December rain crust is up to 10 cm thick, down 100-200 cm in the snowpack, and exists to an average of 1400 m in elevation. While this layer had generally gone dormant in the region through the cold period, it still has the possibility of waking up and will be tested this week with the forecast warming event and ongoing snow accumulation. Extra caution is necessary while the snowpack undergoes this substantial warming after the prolonged period of cold conditions. 

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
• Extra caution for areas experiencing rapidly warming temperatures for the first time.
• Avoid avalanche terrain during periods of strong sun.