Avalanche Forecast

Issued: Jan 27th, 2018 4:54PM

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

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Sunday: 10-15 cm snow. Moderate southerly winds. Alpine temperature near -5.Monday: 15-20 cm snow. Moderate to strong south-westerly winds. Alpine temperature warming in the afternoon to near -1.Tuesday: 5-15 cm snow. Moderate south-easterly winds. Alpine temperature near -5. 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. 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. Persistent slabs to Size 3 were also reported on Friday, remote-triggered by humans and also directly triggered by explosives.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

The current snowpack is complex, with three active weak layers that we are monitoring.60-90 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at treeline elevations and possibly higher. 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 80 to 100 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Snowpack tests show sudden fracture characters and signs of instability such as whumpfs, cracking and avalanches. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It is most problematic at and below tree line. A rain crust buried in November is generally 150 to 200 cm deep.

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

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.
Make conservative terrain choices.Avoid steep convexities or areas with a thin or variable snowpack.Avoid open slopes and convex rolls where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

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