Avalanche Forecast

Issued: Jan 19th, 2018 5:10PM

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.

cgarritty, Avalanche Canada

South Rockies.

Winds are driving the avalanche danger. Seek out low density new snow that winds haven't transformed into a slab. Low consequence terrain is still advised while deeper persistent slab problems remain a real concern.

Summary

Confidence

Moderate -

Weather Forecast

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate to strong southwest winds. Freezing level near valley bottom with alpine high temperatures around -7.Sunday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Strong to extreme southwest winds. Freezing level near valley bottom with alpine high temperatures of -7.Monday: A mix of sun and cloud. Strong west winds. Freezing level near valley bottom with alpine high temperatures of -8.

Avalanche Summary

Only one new natural storm slab release (Size 1.5) has been reported since Thursday's storm. The slab depth was roughly 20cm and it 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 Thursday has buried both a new layer of feathery surface hoar that has been developing 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 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. Slabs may fail on this layer under the weight of a person or machine. Deeper in the snowpack, an early-season rain crust and sugary facets exist. Storm slab releases could step down to these deeper layers to create a large and destructive avalanche. 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

Storm Slabs

Fresh storm slabs have formed over a new weak layer. Sustained southwest winds are likely to make slabs increasingly thick and reactive in lee areas. A storm slab release may have the force needed to trigger a deeper persistent weak layer.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of unstable snowpack.Southwest winds will likely form thicker, more sensitive slabs on northeast aspects.If triggered, storm slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Large avalanches may be triggered on a number of 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.

Back off if you encounter whumpfing, hollow sounds, or shooting cracks.Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Jan 20th, 2018 2:00PM