Weak sugary facetted snow in the bottom third of the snowpack continues to be a concern for triggering large avalanches.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Sunday
Weather Forecast
Tonight: Overcast with light west winds, flurries, and alpine temperatures -15. Saturday: Overcast with light snow and periods of intense flurries. Expect 3-5 cm of new snow combined with moderate westerly winds. Sunday: Overcast with light easterly winds and 5-8 cm of new snow, and alpine temperatures -15. Monday: Overcast with flurries and southerly winds.
Avalanche Summary
The recent storm snow has not settled into a cohesive slab, and remains loose, light, and dry. Some loose dry avalanches to size 1.5 were observed on Friday in the Elk Valley North, near Crown Mountain. Slope testing in the Crowsnest North on Thursday did not produce any shears or signs of instability. One old storm snow avalanche was reported size 1.5 that probably released during the storm. The deep persistent slab problem is a low probability/high consequence scenario that warrants extra caution around large open slopes, especially in shallow snowpack areas. There was a report on Tuesday of a size 3.5 avalanche at Mt Hosmer in the Lizard/Flathead region that released on or stepped down to the deep weak layer near the ground. On Wednesday we had a report from the Lizard range of another size 3.0 deep persistent avalanche on a northeast aspect in the alpine. Avalanche activity on Wednesday near Elkford was limited to loose snow up to size 1.5.
Snowpack Summary
In Elk Valley North on Friday, there was 3cm of new snow and 18 cm of light dry recent storm snow. The mid-pack in this location was well settled, but the bottom third of the snowpack was weak facets. Snow profile tests produced a moderate compression test that released in a sudden planar fashion down 75 cm on the facetted crystals. In the Crowsnest North on Thursday there was 15 cm of new snow, and 35 cm of recent storm snow above various old surfaces. The winds were reported to have been light from the west, and there was not a lot of evidence of wind transport. Near Elkford on Wednesday there was 20 cm of storm snow above a melt/freeze crust that developed from the rain last weekend. The height of snow was 170 cm and there was about 100-120 cm of settled snow above the weak layer of sugary facets that developed during the cold spell in December. Snow profile tests resulted in a hard shear in this location where the facets were sitting on a hard wind crust. Recent slope testing did not show any results. Some loose snow had released naturally from steep unsupported terrain.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.