Avalanche Forecast
Issued: Feb 4th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Deep Persistent Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Reactive storm slabs may be evident underfoot, particularly in wind-loaded areas, but keep the potential for large, destructive deep persistent avalanches in the forefront of your mind.
Summary
Confidence
Avalanche Summary
On Friday, numerous natural wind slabs were observed in the alpine and treeline up to size 2.5. One very large (size 4) deep persistent slab was observed on a south aspect in the alpine.
On Thursday, numerous natural and human-triggered storm and wind slabs were observed throughout the region up to size 2.5. One natural persistent slab avalanche (size 2.5) was observed in the Valhalla mountains. It initiated as a wind slab, stepped down to mid-snowpack weak layers, and then gouged to the basal facets, stepping down to the ground.
Last weekend, various deep persistent slab avalanches were also triggered naturally, being large to very large (size 2 to 4). The avalanches occurred on all aspects between 2400 and 2800 m.
High-consequence avalanche activity is ongoing for several weeks now. Most of the avalanches over the past week were released between 1800 and 2800 m, on all aspects.
Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.
See more on the potential of triggering deeper weak layers in Forecasters' Blog.
Snowpack Summary
Stormy weather over the past week has brought 30 to 80 cm of new snow to the region. Snowfall will continue throughout the day bringing an additional 5-15 cm. Warm windy weather is causing this storm to settle into reactive slabs, especially on leeward slopes that may see more loading from the wind. This storm snow sits above a plethora of old snow surfaces including previously wind-affected snow at upper elevations, a sun crust on steep solar aspects, faceted snow, and surface hoar crystals in wind-sheltered terrain.
Below the recent snow is a crust that extends up to 1800 m in the northern part of the region and up to 2000 m further south. This crust is buried about 40 to 100 cm deep and may host small facets on the crust.
Deeper in the snowpack two layers of surface hoar which formed in early January are 60 to 120 cm deep. These weak layers are still on our radar, although snowpack tests are indicating they may be strengthening.
Large and weak facets from November are near the base of the snowpack, which continue to produce very large avalanches in the region, as described in the Avalanche Summary.
Weather Summary
Saturday night
Cloudy with clear periods and isolated flurries, up to 5 cm accumulation. Alpine temperatures drop to a low of -5 °C. Mostly light ridge wind occasionally gusting to 40 km/h from the southwest. Freezing level drops to 500-1000 metres.
Sunday
Cloudy with snowfall, 5-10 cm accumulation. Alpine temperatures reach a high of -2 °C. Mostly light ridge wind occasionally gusting to 45 km/h from the southwest. Freezing level 1300 metres.
Monday
Cloudy with snowfall, 2-10 cm accumulation Alpine temperatures reach a high of -3 °C. Ridge wind 25 to 55 km/h from the southwest. Freezing level 1400 metres.
Tuesday
Cloudy with snowfall, 5-10 cm accumulation. Alpine temperatures reach a high of -1 °C. Ridge wind southwest 30 to 50 km/h. Freezing level 1600 metres.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be mindful that deep instabilities are still present and have produced recent large avalanches.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Storm Slabs
This week's 40-80 cm of storm snow combined with the strong southwesterly wind and warming temperatures will form reactive storm slabs, especially on leeward slopes that may see more loading from the wind. Dry loose avalanches and sluffing will occur from steep terrain.
Keep in mind that storm slabs have the potential to step down to deeper weak layers, resulting in large and consequential avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A layer of large and weak facets sits near the base of the snowpack. This layer continues to produce very large avalanches that can travel far. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain, or by triggering a smaller avalanche that could step down to this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Numerous problematic weak layers exist in the top meter of the snowpack. Recent observations suggest these layers are gaining strength, but we would continue to be cautious around steep openings within and near treeline elevations as active loading continues. These layers have been most prevalent in the southern part of the region.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 5th, 2023 4:00PM
