Avalanche Forecast
Issued: Dec 5th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
wlewis,
Avalanche Canada
Several weak layers exist in the Purcell snowpack. Stick to simple terrain and exercise careful route-finding in avalanche terrain.
Summary
Confidence
Weather Forecast
SUNDAY NIGHT: Partially cloudy. Moderate westerly winds. Freezing level valley bottom.
MONDAY: Partly cloudy with isolated flurries. Strong westerly winds. Alpine high temperature -12 C. Freezing level valley bottom.
TUESDAY: Increasing cloud. Moderate to strong southwest winds. Alpine high temperature -12 C. Freezing level valley bottom.
WEDNESDAY: Cloudy with strong westerly winds and light snow. Freezing level below 1000m.
Avalanche Summary
The Purcells currently has a complex snowpack - with several reactive persistent weak layers in the mid and lower snowpack.
Two Mountain Information Network (MIN) reports (MIN 1 and MIN 2) on Friday, Dec 3 from Quartz Creek report deep persistent avalanches failing at the base of the snowpack. While its unknown if the images MIN 2 cover the same rider-triggered avalanche avalanche reported in MIN 1, they certainly highlight weak and reactive snow at the base of the snowpack.
A MIN report submitted yesterday from the Brewer Creek area reported a column test failure on the Nov 21 SH down 60cm. Several avalanches that occurred in the Toby Creek drainage last week are thought to have failed on the same layer. This is believed to be lurking around the Toby Creek drainage area, however data is sparse this early in the season and this layer is believed to extend to other areas.
The recent pounding from the atmospheric river delivered heavy precipitation, strong winds, and warm weather. Widespread natural avalanches were observed following each wave of the storm, up to size 3. Explosive control work throughout also produced storm slab avalanches to size 2.5.
Snowpack Summary
10-40cm of low density snow sits over a supportive melt freeze crust, observed up to 2400m. Westerly winds have redistributed new snow into deeper deposits in wind loaded features at higher elevations.
A surface hoar layer extends throughout the Toby Creek drainage and surrounding areas - down 30 to 60 cm in sheltered features at treeline and below. Recent snowpack testing has shown this layer to produce sudden propagating fractures. We have limited knowledge of the distribution of this layer, but suspect is its most active between 1900-2400 m.
A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been recently reactive to human and explosive triggers, and is reactive to snowpack tests. This layer is widespread throughout the region and will likely continue to be a layer of concern.
Average snowpack depth at treeline is 100-180cm, with the deepest snowpack found near the Bugaboos.
Terrain and Travel
- In times of uncertainty conservative terrain choices are our best defense.
- Be alert to conditions that change with elevation and wind exposure.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Wind Slabs
Moderate to strong west and southwest winds continue to build wind slabs in the alpine and treeline. Watch for reactive wind slabs around ridges and loaded terrain features. Recent wind patterns have been variable, slopes may be reverse loaded.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A reactive surface hoar layer exists 20-60cm deep in the Toby Creek drainage and surrounding areas. It is most reactive between 1900-2400 m. This interface may result in larger avalanches, wider propagation and slabs that are more sensitive to human triggers.
Investigate the slab and layer below before committing to steep terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A weak and reactive layer of facets and depth hoar exists at the base of the snowpack above 1900m. While this layer sits deep in the snowpack it has the potential of producing large and destructive avalanches.
Avoid thin rocky start zones where this layer may sit closer to the surface.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 6th, 2021 4:00PM
