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Avalanche Forecast

Archived

Dec 9th, 2019–Dec 10th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

The snowpack structure is unusually shallow and weak for this region. Highly variable thickness of windslab allows for triggering avalanches from thin spots.

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

MONDAY NIGHT: Cloudy with clear periods, light wind from the southwest, alpine temperatures around +3 C, freezing level at 2600 m with a weak temperature inversion.

TUESDAY: Cloudy with flurries, up to 5 cm of snow, 50 km/h wind from the southwest, alpine high temperatures around -2 C, freezing level lowering to 1100 m.

WEDNESDAY: Cloudy with flurries, 50 km/h wind from the south, alpine high temperatures around -4 C, freezing level at 1000 m.

THURSDAY: Cloudy, 20-40 cm of snow, 40 km/h wind from the southwest, alpine high temperatures around -4 C, freezing level at 1000 m.

Avalanche Summary

On Sunday, a few natural and skier triggered slab avalanches of size 1-2 were observed. Several explosive triggered slab avalanches and cornices to size 1-2 were reported. The cornices triggered small slabs on the slopes below which were up to 30 cm thick and ran on a facet/crust layer.

On Saturday, several natural avalanches up to size 2 were reported. A small slab avalanche (size 1.5) was triggered remotely by skiers on an unsupported north facing slope in the alpine. It was 20-30 cm thick. 

Snowpack Summary

Strong southerly winds transported the recent storm snow. This new snow layer is 10 - 70 cm thick depending on the amount of wind affect. Underneath this new snow is a hard crust that formed in late November. The snow above this crust is weak and provides a bed surface for avalanches to run on. Recent snowpack tests have shown notable results on this facet/crust layer. Whumpfing and shooting cracks were reported in the alpine. The snowpack we are seeing at the moment is unusually shallow and weak for the Sea to Sky region.

Currently, typical snowpack depths in the alpine range between 50 and 180 cm, depending on the amount of wind affect. Snowpack depths taper quickly with elevation as most below treeline terrain is still below the threshold for avalanches.

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.