Purcells

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.

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.

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. 

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.

• 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.