Avalanche Forecast
Issued: Mar 5th, 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. Avoid wind-loaded features at upper elevations and steer well clear of overhead cornices and sun-affected slopes during periods of strong solar radiation. The best and safest riding will be found in sheltered and shaded locations.
Check out the most recent Forecaster Blog for the latest on the deep persistent slab problem.
Summary
Confidence
Avalanche Summary
During the storm last week, a natural avalanche cycle occurred with storm slabs reported up to size 3.5. Numerous human-triggered storm and wind slab avalanches were reported up to size 2.
As southwest wind increased on Thursday, natural activity continued to be reported, primarily from wind-loaded terrain in the alpine and treeline up to size 3.5. Human-triggered storm slabs continued to be reported on all aspects.
As skies cleared into the weekend, strong solar input initiated loose dry avalanches from steep solar aspects up to size 2. Numerous cornice failures occurred to size 2.5, some pulling small slabs on the slope below. Human-triggering began to taper, but a few storm and wind slabs were reported from steep, unsupported features in the alpine and treeline.
Explosive control on Saturday produced numerous large persistent and deep persistent slabs up to size 4 on a variety of aspects in the alpine.
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 thin sun crust can be found on 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 lower-density storm snow from last week, hard wind-affected snow in exposed areas and a sun crust on steep solar aspects. The remainder of the mid-snowpack is generally strong with a small surface hoar layer from mid-February that appears to be spotty and has not produced any recent avalanche activity.
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.
TuesdayWeather Summary
Sunday night
Cloudy with clear periods. Alpine temperatures drop to a low of -10 °C. Ridge wind calm to 25 km/h from the southeast. Freezing level at valley bottom.
Monday
Sunny with cloudy periods and isolated flurries. Alpine temperatures reach a high of -8 °C. Ridge wind light from the southeast. Freezing level rising to 400 meters.
Tuesday
A mix of sun and cloud. Alpine temperatures reach a high of -8 °C. Ridge wind southeast 10-25 km/h. Freezing level rising to 900 meters.
Wednesday
Sunny with cloudy periods. Alpine temperatures reach a high of -7 °C. Ridge wind light from the southeast. Freezing level rising to 1000 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.
- 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
Last week's snow fell with moderate to strong southwest winds, which recently switched to northeast. Wind slabs will exist on a variety of aspects in the alpine and exposed areas at treeline and riders should be cautious of the reverse loading pattern with the recent northerly winds.
Sheltered terrain may still produce loose dry avalanches - be prepared to manage your sluff.
Avoid sun-affected slopes in areas that see clear skies and strong sun. Surface snow may rapidly lose cohesion.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Buried weak layers of surface hoar and facets are capable of producing large avalanches.
Manage your terrain choices to minimize exposure to this problem. Avoid large open slopes where avalanches can propagate widely, and be cautious around sheltered terrain features where surface hoar may persist especially convex rolls.
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 6th, 2023 4:00PM
