Avalanche Forecast
Issued: Jan 29th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
kdevine,
Avalanche Canada
Lingering pockets of wind-drifted snow remain a concern for Thursday at higher elevations. Seek out sheltered slopes and watch for reactive wind slabs around steep rolls and ridge features.
Summary
Confidence
Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
WEDNESDAY NIGHT - Cloudy with clear periods and isolated flurries / southwest wind, 20-40 km/h / alpine low temperature near -10
THURSDAY - Cloudy with sunny periods / southwest wind, 20-40 km/h / alpine high temperature near -5 / freezing level 1000 m
FRIDAY - Snow, 15-20 cm / southwest wind, 20-50 km/h / alpine high temperature near -2 / freezing level 2100 m
SATURDAY - Snow, 10-20 cm / southwest wind, 40-70 km/h / alpine high temperature near -3 / freezing level 1600 m
Avalanche Summary
On Sunday there were three deep persistent slab avalanches reported in the region. Two were triggered by explosives, but one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer.
Over the past week there have been a few reports everyday of natural, human and explosives triggered storm slab and wind slab avalanches up to size 3, but mostly around size 1-2. These have occurred on all aspects, mainly at treeline and alpine elevations. The peak of this activity occurred on Saturday and has been tapering since. Wind loaded areas at treeline and in the alpine remain the most likely places to trigger an avalanche.
Snowpack Summary
The Purcells have seen around 20-30 cm of new snow over the past week, with moderate to strong southwest winds, and warm temperatures, which has promoted wind slab development at alpine and treeline elevations.
Below about 1300 m the snow surface is likely moist or wet.
A weak layer of surface hoar can be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, and 100 cm deep along Kootenay Lake.
As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.
Terrain and Travel
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Problems
Wind Slabs
Wind slabs will likely be the most reactive in lee terrain features at upper elevations.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
Triggering deep persistent slab avalanches is a relatively low likelihood but high consequence problem that is most likely in shallow, rocky start zones. Smaller wind slab avalanches could step down to this deeper layer, resulting in a very large avalanche.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 30th, 2020 5:00PM
