Avalanche Forecast

Issued: Mar 7th, 2017 4:22PM

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.

cam_c, Avalanche Canada

Purcells.

Storm slabs are primed for people triggering large avalanches, and have the potential to step down to deeper persistent weaknesses resulting in very large and dangerous avalanches.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

WEDNESDAY: Overcast with light snow resulting in 3-5 cm of new snow combined with light southwest winds.THURSDAY: A mix of sun and cloud with increasing cloud and wind late in the day as the next system moves into the region.FRIDAY: Cloudy with 15-20cm of fresh snow accompanied by moderate SW winds. Alpine temperatures reaching -5 C.

Avalanche Summary

On Sunday and Monday, natural storm and wind slab avalanches were reported up to size 3.0, and explosives control resulted in storm slab avalanches up to size 3.0.

Snowpack Summary

A wide ranging 40-100 cm of fresh snow has fallen in the past week, which is bonding poorly to weak faceted snow and small surface hoar. Moderate to strong southerly winds have formed touchy slabs at all elevations with multiple weaknesses within and under this recent storm snow. Below this is the persistent weakness buried mid-February, which is now down 60-120 cm and composed of a thick rain crust up to about 2000 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. This layer has produced easy results in recent snowpack tests and has proven especially reactive on steep southerly aspects. Several deeper persistent weaknesses also remain a concern, including surface hoar buried early-February (70-130 cm deep), and mid-January (over a metre deep primarily in the northern Purcells ). Basal facets may still be reactive in shallow, rocky start zones.

Problems

Storm Slabs

Weaknesses within and under the 40-100 cm of recent storm snow are susceptible to human triggering. These storm slabs are particularly deep and touchy on slopes loaded by southerly winds.

If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Be alert to conditions that change with elevation.Be increasingly cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Persistent Slabs

Several persistent weak layers buried 75-140 cm deep remain a concern, especially while touchier storm slabs carry the risk of 'stepping down' to one of these deeper weak layers. The greatest risk exists in shallow snowpack areas.

Be aware of overhead hazards and avoid lingering in runout zones.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.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 8th, 2017 2:00PM