Avalanche Forecast

Issued: Dec 3rd, 2018 4:39PM

The alpine rating is moderate, the treeline rating is moderate, 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 susceptible to human triggers where they sit above a buried weak layer. Field observations are limited, so it is critical to supplement this forecast with your own observations.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY NIGHT - Cloudy with clear periods / light northwest winds / alpine temperatures near -12TUESDAY - A mix of sun and cloud / light west to northwest winds / alpine temperatures near -10WEDNESDAY - A mix of sun and cloud / light northerly winds / alpine high temperatures near -10, low temperatures near -15THURSDAY - Sunny with cloudy periods / alpine high temperatures near -6, low temperatures near -10

Avalanche Summary

No new avalanches have been reported in the region, however field observations are very limited. If you have been in the backcountry, please submit your observations to the Mountain Information Network.

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 northerly and northeasterly slopes. There are two layers of surface hoar (weak feathery crystals) being reported in the top 35-40cm. 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.In shallow snowpack areas, the bottom half of the snowpack is reportedly weak and "hollow" feeling on shady aspects due to sugary, faceted snow.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.

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.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

A combination of crust and faceted (sugary) snow exists at the base of the snowpack in the alpine. 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 - 3

Valid until: Dec 4th, 2018 2:00PM