Purcells

As southwest wind picks up in the alpine Thursday afternoon you need to watch for the formation of fresh wind slabs which will add to the existing wind slab problems. The best riding will be found in wind sheltered areas.

Southwesterly flow starts setting up to deliver dribs and drabs of snow and a rising freezing level.

WEDNESDAY NIGHT: Freezing level at valley bottom, light north/northwest wind, no snow expected.

THURSDAY: A few clouds at dawn building to scattered cloud cover in the afternoon, light southwest wind for most of the day with wind speeds picking up at the highest elevations in the later afternoon, no snow expected during the day, trace of snow possible Thursday night.

FRIDAY: Broken cloud cover, freezing level rising to about 800 m, light west/southwest wind at most elevations with some strong west/southwest wind at the higher ridgetops, trace of snow possible.

SATURDAY: Broken cloud cover, freezing level rising to about 1000 m, light west wind at most elevations with some moderate west wind at the higher ridgetops, trace of snow possible.

Since Monday, there have been several reports of small dry loose avalanches initiating from rocks on solar aspects or in steep terrain.

Over the weekend, observers reported large cornice falls and several small to large (up to size 2) natural and skier-triggered wind slab avalanches on westerly aspects above 2400 m. An explosive triggered avalanche reportedly stepped down to a deeper layer. 

Earlier in February, there were a few reports of large avalanches (size 2.5-3) on southeast aspects in the alpine, likely releasing on a layer of facets on a crust (see a photo here), and a large human-triggered avalanche (size 2.5) on surface hoar near Quartz Creek.

Winds have varied in strength and direction over the past week, loading cornices and forming shallow wind slabs at upper elevations that may be possible to trigger. Watch for these wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. Wind slabs may overlie weak, sugary, faceted snow, meaning that they could break wider than expected and will likely be slow to bond. 

In wind-sheltered areas, the upper snowpack is becoming soft and faceted with the cold temperatures and the riding looks pretty good. A weak layer that formed in late January is now 30-60 cm deep. In the northern Purcells this layer has been reported as a surface hoar layer at treeline and below treeline elevations, but a combination of facets on crusts could exist at all elevations throughout the region. 

The northern Purcells also have an older surface hoar layer that can still be found 60-100 cm deep at treeline. Additional weak layers may exist near the bottom of the snowpack and should be considered in steep rocky areas with a shallow or thin to thick snowpack.

• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Approach lee and cross-loaded slopes with caution.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.