Avalanche Forecast
Issued: Mar 5th, 2020 5:00PM
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.
astclair,
Avalanche Canada
There is a high degree of variability through the region. Avalanche danger is highest in the north and west where a persistent weak layer is active and recent snow and wind have formed reactive wind slabs. In drier eastern areas, avalanche danger may be a step lower.
Summary
Confidence
Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.
Weather Forecast
Thursday night: Mostly cloudy, convective flurries with up to 5 cm of snow, moderate southwest winds, alpine temperature -5 C, freezing level 1000 m.
Friday: Cloudy, convective flurries with up to 10 cm snow, light to moderate southwest wind, alpine high temperature -1 C, freezing level 1500 m.
Saturday: Cloudy, 5-10 cm new snow, light southwest wind, alpine high temperature -4 C, freezing level 500 m.
Sunday: Mostly cloudy, another 5-10 cm of snow overnight, light southwest winds, alpine high temperature -5 C, freezing level 500 m.
Avalanche Summary
Over the past several days, small to large (size 1-2) natural, human-triggered, and explosive-triggered avalanches have been observed breaking 25-80 cm deep in the recent storm snow. A few large (size 2) cornices were also observed failing naturally.
Since the weekend, persistent slab avalanches have been observed in the west of the region, where the most snow has accumulated over the surface hoar. Both human-triggered and remotely-triggered avalanches have been reported, even as professionals tiptoe around and avoid suspect terrain features. The problem is touchy but tricky. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab.Â
Snowpack Summary
Convective snowfall and strong winds are building fresh wind slabs in the alpine and open areas at treeline.
A weak layer of surface hoar sits 30-70 cm deep. It may sit over a crust on solar aspects. The distribution of this weak layer and the amount of snow above it varies widely across the region. Incremental loading from successive storms, strong winds, and mild temperatures have strengthened the slab character and increased the depth of the snow above, creating the potential for larger avalanches with serious consequences. Read more about surface hoar on our forecaster blog!
Deep basal facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones. No activity has been observed on this layer since Feb 21.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Wind Slabs
Incremental snowfall and strong winds are building fresh wind slabs in the alpine and open areas at treeline. Wind slabs will be deepest and most reactive in the north and west of the region. If triggered, windslabs have the potential to trigger deeper weak layers.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar sits 30-70 cm deep. So far, this layer has been most reactive at treeline and alpine elevations in the deeper snowpack areas in the west of the forecast region. Where this layer exists, avalanche activity is expected to become more likely as it approaches critical loading by new snow and wind.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Weak snow at the bottom of the snowpack continues to pose a deep persistent slab avalanche problem. Treat wind scoured, rocky, shallow terrain as suspect. Also avoid big alpine slopes that are threatened by cornices overhead.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 6th, 2020 4:00PM
