Avalanche Forecast

Issued: Jan 11th, 2022 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs, Persistent Slabs and Loose Wet.

Avalanche Canada rbuhler, Avalanche Canada

Email

A touchy storm slab with warming temperatures is creating tricky avalanche conditions and old weak layers deep in the snowpack have the potential to wake up this week. Use extra caution around steep south facing slopes in the afternoon if the sun is shining brightly. 

Summary

Confidence

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

Weather Forecast

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. 

Avalanche Summary

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. 

Snowpack Summary

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. 

Terrain and Travel

  • 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.

Problems

Storm Slabs

An icon showing Storm Slabs

40-80 cm of recent storm snow is expected to remain reactive to human triggering on Tuesday, especially in wind loaded terrain. This storm snow may overlie a weak layer and storm slabs may remain reactive for longer than normal. Warming temperatures may also increase the reactivity of the storm snow. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

Deeply buried weak layers in the snowpack will get tested this week with substantial warming and ongoing snow loading. While these layers have been dormant through the extended cold period, they have the potential to wake up this week, and smaller storm slab avalanches have the potential to step down to a deeper layer. Use extra caution and give the snowpack time to adjust to the warm conditions. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Loose Wet

An icon showing Loose Wet

Warming temperatures at lower elevations have likely destabilized the upper snowpack and loose wet avalanches should be expected on steep terrain features. If it is sunny in the afternoon, extra caution is necessary around steep south facing slopes. 

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Jan 12th, 2022 4:00PM