Avalanche Forecast

Issued: Jan 27th, 2018 5:06PM

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.

Avalanche Canada mgrist, Avalanche Canada

Conditions are tricky with an increasing load over multiple weak layers in the snowpack. Take a conservative approach to your terrain choices. If you see more than 30cm of new snow, consider the danger to be HIGH.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Sunday: 10-15 cm snow. Moderate south-westerly winds. Alpine temperature near -6.Monday: 20-30 cm snow. Moderate to strong south-westerly winds. Alpine temperature warming to near -2. Freezing level 1700m.Tuesday: 10-15 cm snow. Moderate south-easterly winds. Alpine temperature near -10. More information can be found in the Mountain Weather Forecast.

Avalanche Summary

On Saturday we received preliminary reports of a human-triggered Size 2.5 avalanche in Glacier National park, on a south east aspect near 2400m. Also on Saturday we received reports of heavy snowfall in the Monashees with 30 cm accumulating in 5 hours! A widespread natural avalanche cycle occurred in these areas Saturday afternoon. Although the spike of avalanche activity from Wednesday has decreased, on Friday we still received reports of storm slabs to Size 2.5 running on northerly aspects above 1900m. Several persistent slabs to Size 3 were also reported on Friday, running naturally and also directly triggered by explosives (and showing good propagation).With incremental loading on Sunday, human triggering will remain likely and avalanches could be surprisingly large due to the structure of the snowpack.

Snowpack Summary

Some areas in the Monashees received significantly more snow (30cm +) than was forecast on Saturday, resulting in a widespread natural avalanche cycle in the afternoon. Elsewhere in the region, 70 to 100 cm of storm snow sits on a layer of crust and/or surface hoar from mid-January. The crust is widespread, with the possible exception of high elevation north aspects. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline.Deeper in the snowpack, the early-January persistent weak layer is buried 70 to 110 cm deep. 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. Yet another persistent weak layer buried mid-December is 100 to 150 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 150 to 200 cm deep. While generally considered dormant, occasional activity has shown that it may react where it is less deeply buried.

Problems

Storm Slabs

An icon showing 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.
If triggered storm/wind slabs may step down to deeper layers and result in very large avalanches.Be very cautious as you transition into wind affected terrain, as wind slabs may be deep and touchy.Be aware of the potential for wide propagations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing 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.Make conservative terrain choices, remembering avalanches may be surprisingly large.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 28th, 2018 2:00PM