Avalanche Forecast

Archived

Dec 8th, 2021–Dec 9th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Northwest Coastal.

Conservative terrain travel will be imperative as fresh wind slabs will remain reactive to rider triggering, particularly where they overlie a weak layer or a crust.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Unsettled weather will continue over the next few days. On Friday, a strong pacific system will move into the northwest ranges bringing strong winds, rising freezing levels, and up to 80 cm of new snow.

Wednesday Overnight: Mainly cloudy, will tapering snowfall, another 5-15 cm can be expected overnight. Continued moderate to strong ridgetop winds from the west. Freezing levels at valley bottom with alpine temperatures around -10 C.

Thursday: Partially cloudy with isolated flurries, accumulation up to 15 cm. Moderate to strong westerly ridgetop winds, freezing levels at valley bottom with alpine temperatures around -10 C.

Friday: We will start to see the affects of a strong pacific system in the early morning. Strong to extreme ridgetop winds from the southwest will accompany 30-60 cm of new snow overnight and into the day. Freezing levels rising to around 700m, alpine temperatures around -5 C.

Saturday: Continued snowfall with another 10-20 cm of accumulation. Winds easing moderate to strong from the southwest at ridgetop, freezing levels dropping to valley bottom, and alpine temperatures around -10 C.

Avalanche Summary

On Monday, a size 2 skier-accidental was reported on a south aspect at treeline in the Blue Boy area in the Shames backcountry. The avalanche character is unknown, either shallow wind slab or loose dry. See full report here.

Expect natural and rider triggered avalanches to occur as new snow continues to be redistributed by wind. If you do head out in the backcountry, please share your observations to the Mountain Information Network!

Snowpack Summary

20-50 cm of storm snow will continue to be redistributed by moderate to strong westerly winds into wind slabs in the alpine and treeline. Below this new snow, a weak layer of surface hoar or facets may be found from previous cold temperatures and clear skies. This weak layer will add to the reactivity of new wind slabs, especially where they are sitting on a crust.

Snowpack depths range from 150 cm- 300 cm at treeline and 200 cm- 400 cm in the alpine. The Dec 1st crust extends up to 2000m in the southwest of the region, but may only be found to around 1200m in the Terrace area. This crust is down 70-100cm in sheltered areas.

Terrain and Travel

Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
Investigate the bond of the recent snow
Stay off recently wind loaded slopes until they have had a chance to stabilize.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.