Avalanche Forecast
Issued: Feb 5th, 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.
lbaker,
Avalanche Canada
Southwest winds and warm temperatures are promoting slab cohesion and building reactive storm slabs in lees. Be especially cautious as you transition into wind-affected terrain and remember that if triggered storm slabs in motion could step down to deeper weak layers and result in very large avalanches.
Summary
Confidence
Avalanche Summary
On Saturday, numerous natural storm slab avalanches were reported throughout the region to size 3. Storm slabs were particularly touchy between 1800 m and 2400 m on north and east aspects in lee areas. A skier accidental storm slab avalanche size 2.5 was reported on an east aspect at 2350 m.
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.
High-consequence avalanche activity is ongoing for several weeks now. Most of the avalanches over the past week 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. 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
Sunday Night
Mainly cloudy with clear periods and isolated flurries, trace accumulation. Alpine temperatures reach a high of -2 °C. Northwesterly ridge wind 20-40 km/h. Freezing levels fall to 1000 metres.
Monday
Mainly cloudy with isolated flurries, 2-5 cm accumulation. Alpine temperatures reach a high of -3 °C. Westerley ridge wind 20 km/h increasing to 60 km/h from the southwest in the afternoon. Freezing level 1300 metres.
Overnight flurries bring 5-10 cm accumulation.
Tuesday
Cloudy with flurries, 5-10 cm accumulation. Alpine temperatures reach a high of -1 °C. Ridge wind southwest 20 km/h gusting to 60 km/h. Freezing level 1500 metres.
Wednesday
A mix of sun and cloud. Alpine temperatures reach a high of -10 °C. Ridge wind west 20 km/h. Freezing level 1000 metres.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be especially cautious as you transition into wind affected terrain.
- 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 30-80 cm of storm snow combined with the strong southwesterly wind and warming temperatures have formed reactive storm slabs, especially on leeward slopes that may see more loading from the wind.
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 6th, 2023 4:00PM
