Avalanche Forecast

Issued: Dec 4th, 2018 4:11PM

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

kdevine, Avalanche Canada

Purcells.

Wind slabs may be more reactive where they sit above a buried weak layer. Field observations are limited, so it is important to supplement this forecast with your own observations. If you get out, tell us what you see by posting to the MIN! (here)

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TUESDAY NIGHT - Clear periods / light to moderate northerly winds / alpine low temperature -14WEDNESDAY - Sunny with cloudy periods / light easterly winds / alpine high temperature -12THURSDAY - A mix of sun and cloud / light westerly winds / alpine high temperature -6, low temperature -11FRIDAY - Sunny with cloudy periods / light southerly winds / alpine high temperature -5, low temperature -9

Avalanche Summary

One size 1.5 wind slab avalanche was reported on a steep, cross loaded, rocky, north facing feature. Trigger type and elevation are unknown.Field observations in this region are very limited. If you have been in the backcountry, please submit your observations to the Mountain Information Network (MIN)

Snowpack Summary

The early season snowpack is highly variable in the Purcells. Approximately 20 cm of snow fell last week which may have been blown into wind slabs on exposed north and northeast facing slopes. There are two layers of surface hoar (weak feathery crystals) being reported in the top 15-30cm. The surface hoar is most prominent at treeline, but it may be found in sheltered alpine areas. Both of these layers may be associated with a sun crust on south aspects in some areas.A prominent feature of the snowpack is a combination of a crust and faceted (sugary) snow found at or near the base of the snowpack. This layer mainly exists in the alpine but it may be found at upper treeline elevations as well.Total snowpack depths vary greatly throughout the region with anywhere between 70 and 150 cm in the alpine and tapering rapidly at treeline and below. In shallow snowpack areas, the bottom half of the snowpack is reportedly weak and "hollow" feeling on shady aspects due to sugary, faceted snow.

Problems

Wind Slabs

Wind slabs are most likely found on leeward slopes. They will likely be more reactive where they sit above a weak feathery surface hoar layer and/or a sun crust.

If triggered, the slab may step down to deeper layers resulting in large avalanches.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Caution in lee and cross-loaded terrain near ridge crests.

Aspects: North, North East, East, North West.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

A combination of crust and faceted (sugary) snow exists at the base of the snowpack. This layer could produce avalanches on steep, smooth slopes in the alpine.

Large alpine slopes with a thin-thick, rocky snowpack are suspect to triggering.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Dec 5th, 2018 2:00PM