Avalanche Forecast

Issued: Mar 1st, 2017 5:14PM

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.

cgarritty, Avalanche Canada

Purcells.

Be aware of wind slab hazard building over the day on Thursday and take extra caution if you encounter more new snow than is forecast.

Summary

Confidence

Moderate -

Weather Forecast

Thursday: Flurries bringing a trace to 5 cm of new snow. Winds light to moderate from the southwest, gusting to strong in the afternoon. Freezing level to 1400 metres with alpine temperatures of -6.Friday: Periods of snow bringing 10-15 cm of new snow. Winds strong to extreme from the southwest. Freezing level to 1500 metres with alpine temperatures of -5Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Winds moderate from the southwest. Freezing level to 1200 metres with alpine temperatures of -7.

Avalanche Summary

Aside from several Size 1 natural loose dry sluffs from steep terrain reported in the north of the region on Tuesday, no new avalanches have been reported.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, ongoing light snowfall and increasing winds on Thursday are expected to promote new wind slab activity at treeline and in the alpine.

Snowpack Summary

5-15 cm of new snow fell over the region over Tuesday night, burying widely reported faceted surface snow as well as surface hoar recently reported at about 3mm on shaded aspects in some areas. About 25-55 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

Continuing light snowfall will pair with strong high elevation winds to form reactive new wind slabs at treeline and in the alpine. The best and safest riding may be in sheltered, lower-elevation terrain.

Be cautious as you transition into wind affected terrain.Stay off recent wind loaded areas until the slope has had a chance to stabilize.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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 steep convexities or areas with a thin or variable snowpack.Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 2nd, 2017 2:00PM