Avalanche Forecast
Issued: Mar 7th, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
astclair,
Avalanche Canada
Sunny breaks after a week of storms may make wind slabs and cornices more sensitive to failure. A buried weak layer warrants a conservative mindset and terrain use strategy, particularly in the south of the region. Where this layer is absent, danger ratings may be a step lower.
Summary
Confidence
Weather Forecast
Saturday night: Clearing overnight, light variable winds, alpine temperature -15 C..
Sunday: Mix of sun and cloud, light west winds, alpine high temperature -7 C.
Monday: Mostly clear, light southwest winds, alpine high temperature -5 C, freezing level 1000 m.
Tuesday: Increasing cloud, 5-10 cm of snow, moderate to strong south winds, alpine high temperature -4 C, freezing level 1300 m.
Avalanche Summary
Over the past several days, a natural cycle of large to very large (size 2-3) avalanches released in the recent storm snow, primarily on wind-loaded aspects (northeast, east, and southeast) above 1800 m. Several were triggered by large cornices failures. If triggered, wind slabs and cornices could step down to the buried surface hoar layer, forming large avalanches. Use added caution on sun-exposed slopes when the sun is shining, as it could rapidly deteriorate the storm snow and cornices and cause loose or slab avalanches.
Many large to very large avalanches (size 2-3) releasing on the February 22 surface hoar have been observed over the past week. These avalanches primarily occurred on north, northeast, and east aspects between 1400-2100 m and in the southern part of the region. These avalanches have propagated widely across terrain features, warranting conservative terrain margins. Check out this MIN reporting a large, snowmobile-triggered avalanche on Friday for a helpful example.
Snowpack Summary
Incremental snowfall and wind have formed reactive wind slabs in the alpine and open areas at treeline that remain possible to human trigger. Cornices are large and looming after a week of successive storms.
A weak layer of surface hoar may be found 60-100 cm deep. There is uncertainty about the distribution and reactivity of this layer, especially in the north of the region. This MIN from the Trophy Mountains and this MIN from Allan Creek confirm the presence of this layer in the southern half of the region. Sheltered north, northeast, and east facing slopes near treeline are the most suspect. Riders will be capable of triggering this layer for some time until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Use conservative route selection and resist venturing out into complex terrain.
- Stay off recently wind loaded slopes until they have had a chance to stabilize.
- Even brief periods of direct sun could produce natural avalanches.
Problems
Persistent Slabs
A weak layer of surface hoar may be found 60-100 cm deep, within the prime range for human-triggering. Over the past week, large (size 2-3) natural and human-triggered avalanches have released on this layer. Observations are concentrated to north, northeast, and east aspects near treeline. This problem has been observed in all but the northern tip of the region, where there is uncertainty around the distribution of this layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Incremental snowfall with wind has formed wind slabs in the alpine and open areas at treeline.This problem also overlaps with where cornices may be reaching their breaking point. If triggered, wind slabs and cornices could step down to the buried surface hoar layer, forming large avalanches. Use added caution on sun-exposed slopes when the sun is shining, as it could rapidly deteriorate the storm snow and cornices and cause loose or slab avalanches.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 8th, 2020 4:00PM
