Avalanche Forecast
Issued: Mar 14th, 2020 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.
ldreier,
Avalanche Canada
Fresh wind slabs were formed by moderate to strong northeast and east wind at all elevations. The sun is strong at this time of year and can weaken the snowpack. Be especially cautious underneath sun exposed steep slopes and around rock outcrops.
Summary
Confidence
Weather Forecast
Saturday night: Cloudy with clear periods, light east wind, alpine high temperature -22 C, freezing level at valley bottom.
Sunday: Sunny, light northeast wind, alpine high temperature -12 C, freezing level at 700 m.
Monday: Sunny, light northeast wind, alpine high temperature -8 C, freezing level at 1400 m.
Tuesday: Mostly sunny, light northeast wind, alpine high temperature -5 C, freezing level at 1800 m.
Avalanche Summary
Several storm and wind slab avalanches of size small to large (size 1-2.5) were reported during and after the recent storm mid week breaking 20-40 cm deep. Observations have decreased since. Most avalanches released on the old snow surface which may consist of old wind slab, surface hoar or a sun crust on steep solar aspects. Triggered slabs have the potential to step down to the buried surface hoar layer from February 22, creating very large avalanches.
Over the past week, human-triggered and explosive-triggered avalanches releasing on the February 22 surface hoar have been consistently reported from the north and west of the region. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group trigger the slab. These avalanches have been remotely-triggered and have propagated widely across terrain features, warranting conservative terrain margins (see this MIN or this MIN for a helpful example). Observations extend to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity.
Over the past week, professionals reported large (size 2.5 to 3.5) natural and explosive-triggered avalanches releasing on weak layers near the ground. These avalanches occurred on west and north facing slopes above 2500 m, and they confirm that the deep persistent slab problem remains a concern.
Snowpack Summary
Moderate to strong northeast and east wind has redistributed the snow and formed wind slabs at all elevations. The mid week storm snow may sit on a weak surface hoar layer and a sun crust on steep solar aspects.
A weak layer of surface hoar from February 22 may be found 50-100 cm deep. It may sit over a crust on solar aspects. With successive storms, more areas have reached critical loading and developed a slab over this layer. Managing this problem requires a patient and diligent mindset, implemented by avoiding suspect slopes and maintaining conservative terrain margins. This persistent weak layer will likely remain a problem until there is a substantial change in the snowpack. 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.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
Problems
Wind Slabs
Moderate to strong northeast and east wind formed wind slabs at all elevations which might be reactive to human triggers.
The recent storm snow may sit on a weak surface hoar layer and a sun crust on steep solar aspects. Both, storm and wind slabs, may be reactive to human triggers especially where the slab properties increase due to warming temperatures and solar radiation. If triggered, slabs could step down to the buried persistent surface hoar layer, forming large avalanches.
Aspects: North, South East, South, South West, West, North West.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar sits 50-100 cm deep, within the range for human-triggering. Over the past week, large human-triggered avalanches have released on this layer. As more areas approach critical loading from additional snow and wind, human-triggering remains likely.
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 and avoid big alpine slopes that are threatened by cornices overhead.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 15th, 2020 5:00PM
