Weak sugary facetted snow in the bottom third of the snowpack continues to be a concern for triggering large avalanches
Confidence
Moderate - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
SUNDAY: Flurries, accumulation 5-10cm / Alpine temperature -12 °C / Light east windMONDAY: Isolated flurries, accumulation up to 5cm / Light to moderate west wind / Alpine temperature -12TUESDAY: Mix of sun and cloud / Light to Moderate west wind / Alpine temperature -13More details can be found on the Mountain Weather Forecast.
Avalanche Summary
Some loose dry avalanches to size 1.5 were observed on Friday in the Elk Valley North, near Crown Mountain. 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 late last week, up to 20cm of light dry storm snow fell. The mid-pack in this location is well settled, but the bottom third of the snowpack is weak facets. Snow profile tests produced moderate compression tests that released suddenly down 75 cm on the facetted crystals. In the Crowsnest North late last week up to 35 cm of recent storm snow lies above various old surfaces. Near Elkford up to 20 cm of storm snow sits above a melt/freeze crust. Approximately 100-120 cm of settled snow sits above the weak layer of sugary facets that developed during the cold spell in December. Snow profile tests indicate hard shears in this location where the facets are sitting on a hard wind crust.
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.