Avalanche Forecast
Issued: Mar 6th, 2023 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.
zryan,
Avalanche Canada
Don't let good visibility lure you into dangerous terrain. Wind slabs may exist on a variety of aspects due to recently shifting wind direction. The air is cold but the March sun can be strong so avoid exposure to cornices and watch for signs of warming on steep south aspects. Thin rocky areas will remain a concern for triggering deeply buried weak layers in this complex snowpack.
Summary
Confidence
Moderate
Avalanche Summary
During the storm last week, a natural avalanche cycle occurred with storm slabs reported up to size 3.5.
In the past few days, strong solar input has initiated loose dry avalanches from steep solar aspects and cornice failures up to size 2.5, with some of these cornices pulling slabs on the slope below. Several human-triggered storm and wind slabs have been reported on all aspects in steep and unsupported or wind-loaded features in the alpine and treeline.
Explosive control on Saturday and Sunday 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.
Two notable deep persistent slab avalanches occurred on Saturday, both in shallower snowpack areas in the eastern part of the region. One was a size 3 natural that occurred on an east aspect in the alpine. This avalanche occurred on a re-loaded bed surface. The other was a size 3.5 skier-remote avalanche on a shallow, south-facing alpine slope. These avalanches highlight the terrain we are most concerned about triggering deep persistent slabs: shallow, thick-to-thin alpine and upper treeline terrain.
Read more about managing the deep persistent slab problem in our latest Forecaster Blog.
Snowpack Summary
On the surface, a sun crust can be found on steep south-facing aspects and surface hoar growth has been reported in some parts of the region. 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. 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
Monday night
Clear periods. Alpine temperatures drop to a low of -10 °C. Light southeasterly ridge wind. Freezing level at valley bottom.
Tuesday
Sunny with cloudy periods. Alpine temperatures reach a high of -7 °C. Ridge wind southeast 10-25 km/h. Freezing level 500-900 metres.
Wednesday
Mainly sunny. Alpine temperatures reach a high of -6 °C. Ridge wind light from the southeast. Freezing level 700-1100 metres.
Thursday
Sunny with cloudy periods. Alpine temperatures reach a high of -8 °C. Ridge wind light from the southeast. Freezing level 800 metres.
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.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Problems
Wind Slabs
Variable winds over the past week mean that wind slabs could be found on all aspects.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of facets, surface hoar in sheltered areas and on south aspects, a crust can be found down 40-80 cm. This layer is most likely to be triggered on steep south-facing slopes or sparsely treed slopes at treeline and below.
Aspects: All aspects.
Elevations: All elevations.
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 smaller avalanches in motion or cornice failures have the potential to produce very large avalanches with wide propagation. Suspect terrain for human triggering includes steep, shallow and rocky terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 7th, 2023 4:00PM
