Avalanche Forecast

Issued: Jan 22nd, 2018 5:02PM

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.

cgarritty, Avalanche Canada

South Rockies.

Intense southwest winds are driving wind slab formation at all elevations. Persistent slab activity in deeper in the snowpack still can't be written off.

Summary

Confidence

Moderate -

Weather Forecast

Tuesday: Mainly cloudy with isolated flurries and a trace of new snow, continuing overnight. Moderate to strong southwest winds. Alpine high temperatures around -7.Wednesday: Mainly cloudy with continuing scattered flurries and a trace to 5 cm of new snow, continuing overnight. Moderate to strong southwest winds. Freezing level rising to 1600 metres with alpine high temperatures of -3.Thursday: A mix of sun and cloud with lingering isolated flurries and a trace of new snow. Moderate southwest winds. Freezing level returning to valley bottom with alpine high temperatures of -9.

Avalanche Summary

Reports from Saturday showed explosives control in the Castle area producing several Size 2-2.5 storm slabs around 40 cm deep. Ski cutting in the same area produced numerous smaller (Size 1) releases also confined to the recent storm snow.Looking forward, expect ongoing strong winds to promote lee loading as well as slab formation and reactivity even as snowfall tapers off.

Snowpack Summary

Up to 40 cm of new snow from recent stormy weather has buried both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects. Moderate to strong winds have been scouring away the new snow on southwest aspects while continuously loading and building 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.Down about 60-80 cm, weak layer of feathery surface hoar crystals and/or sun crust from mid-December is found at treeline and below treeline elevations. Deeper in the snowpack, another weak early-season layer of rain crust and sugary facets exists. This deeper layer is the most concerning persistent weakness in the South Rockies. It is expected to be particularly sensitive to triggering in variable-depth snowpack areas in the alpine. 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

Cranking southwest winds will continue to scour away our recent snow into increasingly thick and reactive wind slabs in lee areas. Slabs that form in openings at lower elevations may overlie a layer of touchy surface hoar.

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: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

Persistent slab activity has been declining, but potential still exists for large avalanches to be triggered on deeply buried weak layers. Stress on deep weak layers will increase as intense southwest winds continue to load lee areas.

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 23rd, 2018 2:00PM