Avalanche Forecast

Archived

Nov 28th, 2021–Nov 29th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

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

Sea To Sky.

Recent snowfalls at higher elevations have developped storm slabs that could trigger deeper weak layers and produce large avalanches.

Confidence

Low - Uncertainty is due to limitations in the field data.

Weather Forecast

A weak ridge of high pressure will bring a break between storms with mainly quiet conditions for Monday.

Sunday night: Flurries; 10-15 cm. Moderate to strong southwest winds. Alpine low temperatures -3 C with freezing levels going down to 1600 metres.

Monday: Mainly cloudy with isolated flurries. Moderate southwest winds. Alpine high temperatures -3 C with freezing levels steady at 1600 metres.

Tuesday: Heavy snow or rain; 15-30 cm. Strong southwest winds. Alpine high temperatures -3 C with freezing levels at 1700 metres.

Wednesday: Wet snow mixed with rain; 25-35 cm. Strong southwest winds. Alpine high temperatures +1 C with freezing levels at 2200 metres.

Avalanche Summary

A few natural and triggered storm slabs avalanche (size 1) and loose wet were reported Saturday. Also, large avalanches sliding on recently buried surface hoar and deeper buried crusts have been observed in the region as well as in the neighboring South Coast Inland.

Snowpack Summary

Recent snowfalls and strong southerly winds have created reactive storm slabs in leeward alpine and treeline features. The new snow also buried deeply a surface hoar layer observed in between 1800 and 2100 meter and a combo of thick crust/ facets present up to 2200 meters. Surprising large avalanches sliding on these weak layers have been reported over the last few days and, if upper elevations slopes haven't avalanched already, further loading by snow and wind or human triggers could initiate avalanche activity on these layers.

Average snow depths at treeline are now likely closer to 150-200 cm; 250+ cm in the alpine. Snowpack depths decrease dramatically below treeline and may still be below threshold for avalanches in some areas. Early season hazards such as rocks, stumps, and creeks are still a concern at these lower elevations.

Terrain and Travel

In times of uncertainty conservative terrain choices are our best defense.
Be aware of the potential for large, deep avalanches to run full path or even longer.
If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.