Avalanche Forecast

Issued: Jan 26th, 2018 4:19PM

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

pgoddard, Avalanche Canada

Purcells.

Tricky conditions with a slowly increasing load over multiple weak layers in the snowpack. Take a conservative approach to your terrain choices.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Saturday: 5-10 cm snow. Light to moderate south-westerly winds. Alpine temperature near -10. Sunday: 5-10 cm snow. Light south-westerly winds. Alpine temperature near -7.Monday: 5 cm snow. Moderate to strong south-westerly winds. Alpine temperature near -1.More information can be found in the Mountain Weather Forecast.

Avalanche Summary

A widespread natural avalanche cycle was observed on Wednesday, with some natural activity continuing on Thursday. Avalanches up to size 4 were reported from all aspects, many failing on persistent weak layers down 1 m or more. Almost all the persistent slabs failed at elevations above 2000 m. The theme on Thursday was still a very touchy snowpack, with numerous large to very large avalanches triggered by explosives.Natural avalanche activity has now slowed, but the potential for human-triggering of surprisingly large avalanches remains elevated.

Snowpack Summary

The current snowpack is complex, with three active weak layers that we are monitoring.60-100 cm recent storm snow overlies a crust and/or surface hoar layer (from mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10 to 30 mm in size and at all elevation bands. The recent snow fell with strong south winds, producing wind slabs and cornices in lee features. Deeper in the snowpack, a persistent weak layer known as the early-January layer is present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential, as well as other signs of instability such as whumpfs, cracking and avalanches. Another persistent weak layer that was buried mid-December is 60 to 100 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.

Problems

Storm Slabs

Recent snow and wind have built slabs that can be triggered by the weight of a person. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.

Be very cautious as you transition into wind affected terrain, as wind slabs may be deep and touchy.If triggered storm slabs may step down to deeper layers and result in very large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Several weak layers are buried in the snowpack, creating very large avalanches when triggered.

Avoid open slopes and convex rolls where buried surface hoar may be preserved.Avoid thin, rocky or sparsely-treed slopes.Use conservative route selection, bearing in mind that avalanches may be surprisingly large.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 27th, 2018 2:00PM