Avalanche Forecast

Issued: Jan 20th, 2018 4:32PM

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

Avalanche Canada cgarritty, Avalanche Canada

Winds are driving the avalanche danger. Seek out sheltered snow that hasn't been wind-affected for the best, safest skiing and riding.

Summary

Confidence

High -

Weather Forecast

Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow. Strong southwest winds. Alpine high temperatures around -7Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Strong southwest winds. Alpine high temperatures of -8.Tuesday: Cloudy with sunny periods. Moderate southwest winds. Alpine high temperatures of -9.

Avalanche Summary

Reports from the southeast of the region on Friday showed several small (Size 1) loose dry slides releasing with ski cutting in steep terrain around treeline. Only one natural storm slab release (Size 1.5) has been reported since Thursday's storm. The slab depth was roughly 20cm and it also occurred in the southeast of the region. Improving visibility may allow for more observations of recent activity.Looking forward, expect ongoing moderate to strong winds to promote lee loading as well as slab formation and reactivity even as snowfall tapers off.

Snowpack Summary

Up to 30 cm of new snow from last week's storm has buried both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects. The new snow will need time to form a reliable bond to this previous surface. Moderate to strong winds have also been encouraging slab formation at higher elevations and continuously loading loose snow into deeper wind slabs in lee areas. Beneath the new snow, Previous southwest winds formed wind slabs that are now buried in lee terrain at higher elevations.An unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations. Deeper in the snowpack, an early-season rain crust and sugary facets exists. Slabs may still fail on these layers under the weight of a person, a machine, or large wind slab release. Although the snowpack structure is variable across the region, these persistent slab problems are generally widespread. Snowpack depths are across the region are similarly variable, but typically shallower in the east.

Problems

Wind Slabs

An icon showing Wind Slabs
Sustained southwest winds have been transporting recent snow into increasingly thick and reactive wind slabs in lee areas. A wind slab release may have the force needed to trigger a deeper persistent weak layer.
If triggered, wind slabs may step down to deeper layers and result in large avalanches.Southwest winds will likely form thicker, more sensitive slabs on northeast aspects.Whumpfing, shooting cracks and recent avalanches are all strong indicators of unstable snowpack.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Potential still exists for large avalanches to be triggered on deeply buried weak layers, even in fairly dense trees and shallow slope angles. Stress on deep weak layers will increase as southwest winds continue to load lee areas over the weekend.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Jan 21st, 2018 2:00PM

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