Avalanche Forecast

Issued: Jan 5th, 2018 4:26PM

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

mconlan, Avalanche Canada

South Columbia.

A weak layer is buried at a depth prime to human triggering. As the overlying snow forms a slab from new snowfall and warmer air, destructive avalanches will likely result. Cautious route finding is advised, particularly at treeline elevations.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

SATURDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, freezing level near 800 m.SUNDAY: Cloudy with light snowfall, accumulation 2-5 cm, light southwesterly winds, freezing level near valley bottom.MONDAY: Cloudy with light snowfall, accumulation 5-10 cm, light southwesterly winds, freezing level near valley bottom.

Avalanche Summary

Recent natural and skier-triggered avalanches have been reported on the December 15 layer at and below treeline on all aspects. Numerous reports of whumphing were also noted in low elevation cutblocks and flat terrain. Reactivity of the persistent slab is likely to increase with warmer temperatures below treeline as the snow forms slab properties.

Snowpack Summary

A warming trend and new snowfall are creating a dangerous slab above buried weak layers in some areas. Numerous persistent weak layers exist in the snowpack. Dry snow overlies two layers composed of weak and feathery surface hoar, with the deeper layer (December 15) buried 50 to 70 cm. This layer is found most often around and below treeline. As the overlying dry snow becomes more cohesive and forms a slab, this layer has the potential to create easily-triggerable destructive slab avalanches. Where and when this will occur is tricky to predict and even professionals are scratching their heads about it. It is a good time for conservative decision-making.The new snow is falling on variable surfaces, including surface hoar in sheltered slopes, a sun crust on steep solar aspects, and wind effect in exposed alpine and treeline locations.Deeper in the snowpack at depths of about 90 to 150 cm, a rain crust from November is producing variable snowpack test results, from sudden fracture characters to no result. This layer is considered dormant for now, but could be triggered where the snowpack is thin.Please share your observations through the Mountain Information Network.

Problems

Persistent Slabs

Around 50 to 70 cm of snow sits above a touchy weak layer. As this snow settles and gains slab properties, a dangerous slab that is easily triggered will likely form.

Use conservative route selection. Choose moderate-angled and well-supported terrain.Watch for signs of slab formation, such as whumpfing and shooting cracks.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Loose Dry

New snow will likely move easily, as it is falling on a recently buried weak layer and/or a crust.

Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Jan 6th, 2018 2:00PM