Avalanche Forecast

Issued: Feb 28th, 2017 3:44PM

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

Avalanche Canada jlammers, Avalanche Canada

Snowfall amounts for Tuesday night are uncertain. Watch for new wind slabs and pay close attention to how much snow falls in your area.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Tuesday night: 5-15cm of new snow / Extreme westerly winds / Alpine temperatures of about -15Wednesday: 2-4cm of new snow / Strong westerly winds / Alpine temperatures of about -16Thursday: 2-4cm of new snow / Strong southerly winds / Alpine temperatures of about -8Friday: 3-8cm of new snow / Light and variable winds / Alpine temperatures of about -8

Avalanche Summary

Some notable persistent slab avalanches were reported last week. This included natural activity on the western slopes of the Purcells (two size 2.5 avalanches on the February 3rd surface hoar and one size 3.5 avalanche on the November crust) and two large skier triggered avalanches near Golden (including a size 3 remotely-triggered avalanche on the mid-January interface). Triggering a persistent slab avalanche is currently a low probability - high consequence scenario that warrants a cautious approach to terrain. Looking forward, new snow and extreme winds on Tuesday night are expected to promote new wind slab activity at treeline and in the alpine.

Snowpack Summary

By Wednesday morning, new snow and extreme winds are expected to have formed fresh wind slabs at treeline and in the alpine. About 20-40 cm below the surface you'll likely find the mid-February interface which is composed of a thick rain crust up to about 2000 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Several deeper weak layers remain a concern including the February 3rd surface hoar layer (40-80 cm deep) in the southern Purcells, and the mid-January surface hoar layer in the northern Purcells (about 100 cm deep). Basal facets may still be a reactive in shallow rocky start zones.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and extreme winds on Tuesday night are expected to form reactive new wind slabs at treeline and in the alpine. The best and safest riding may be in sheltered, lower-elevation terrain.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Stay off recent wind loaded areas until the slope has had a chance to stabilize.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Several persistent weak layers buried 50-100 cm deep remain a concern (surface hoar, facets, and crusts). Slopes with thin or variable snowpack are the most suspect trigger points.
Avoid lingering in runout zones.Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 1st, 2017 2:00PM