Avalanche Forecast

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

An offshore ridge of high pressure is expected to build on Wednesday bringing a break in the weather before the next storm system arrives on Thursday night. 

Tuesday Overnight: Snowfall at higher elevations 5-15 cm, moderate SW wind, treeline temperature around 0 °C, freezing level as high as 1000 m. 

Wednesday: Mainly cloudy with sunny breaks in the afternoon, moderate to light SW wind, treeline high around 0 °C, freezing level as high as 1100 m. 

Thursday: A mix of sun and cloud, light variable wind, treeline temperature around +2 °C, freezing level as high as 1500 m with a temperature inversion.  

Friday: Potential for heavy snowfall/rainfall, strong S wind, treeline temperature around +2 °C, freezing level as high as 1300 m. 

Early reports from Tuesday suggest that the natural activity has tapered off but a few natural wind slabs were still observed in the north. Explosives were triggering numerous storm slab avalanches on Tuesday morning. At lower elevations, natural loose wet avalanches have started to be reported. 

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 size was 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 so far, it could be an indicator that deeper weaknesses in the snowpack could be waking up with the warming temperatures. 

40-80 cm of storm snow accumulated over the weekend, with the highest amounts along the immediate coastal areas and the north of the region. Recent strong SW winds have redistributed this new snow into wind slabs in exposed 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 new 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.