Avalanche Forecast
Issued: Mar 7th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Deep Persistent Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Cornice failures have the potential to initiate surprisingly large slab avalanches. Steer well clear of overhead hazard and steep solar slopes during periods of strong sun.
Triggering large slab avalanches remains possible in steep, rocky, and wind-affected areas. Sheltered and shaded terrain will offer the best and safest riding.
Summary
Confidence
Moderate
Avalanche Summary
With periods of strong sun in the past few days, several large (size 2-3) natural cornice failures have been noted throughout the region. Some of these cornices pulled slabs on the slopes below that failed on persistent weak layers in the mid or lower snowpack. Several large (size 2-3) natural wind slabs failed in south-facing alpine and treeline terrain in Glacier National Park. One large (size 3) natural deep persistent slab was observed in the alpine north of Revelstoke.
Explosive control last weekend produced numerous large persistent and deep persistent slabs up to size 4 on a variety of aspects in the alpine. Several large cornices were also initiated with explosives.
Read more about managing the deep persistent slab problem in our latest Forecaster Blog.
Snowpack Summary
A dusting of new snow overlies a sun crust on steep south-facing aspects, surface hoar in some areas and widespread near surface-faceting from cold temperatures. Last week's 20-60 cm of storm snow has been redistributed by variable winds in exposed areas creating pockets of wind slab that may be found on all aspects.
This recent storm snow overlies a weak layer of faceted snow and a sun crust on sun-affected slopes. This layer has been noted as a failure plane for some recent avalanche activity, as seen in this MIN report from Saturday. A second weak layer in now down 60-110 cm. It is comprised of a sun curst on solar aspects and surface hoar in isolated sheltered and shaded areas. The remainder of the mid-snowpack is generally strong.
The November facets are still prominent at the base of the snowpack. They are showing signs of rounding but there is still a considerable step in resistance between them and the overlying snow. These facets are most pronounced in shallow rocky areas.
Weather Summary
Tuesday night
Clear with cloudy periods. Alpine temperatures reach a low of -9 °C. Ridge wind light from the southeast. Freezing level at valley bottom.
Wednesday
Sunny with cloudy periods. Alpine temperatures reach a high of -6 °C. Ridge wind light from the southeast. Freezing level rises to 800 meters.
Thursday
Sunny with cloudy periods. Alpine temperatures reach a high of -8 °C. Ridge wind light southeast. Freezing level 700 meters.
Friday
A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -8 °C. Ridge wind light from the southeast. Freezing level 600 meters.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Problems
Wind Slabs
Variable winds over the past week mean that wind slabs could be found on all aspects. Keep your guard up as you enter wind-affected terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth, but large triggers such as cornice failures or smaller avalanches in motion have the potential to produce very large avalanches with surprisingly wide propagation. Suspect terrain for human triggering includes steep, shallow and rocky terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are two layers of concern in the upper and mid-pack. These layers are gaining strength with cold temperatures but could be triggered on steep south-facing slopes where a sun crust is buried or sparsely treed slopes where surface hoar may be preserved.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 8th, 2023 4:00PM
