Avalanche Forecast

Archived

Dec 11th, 2018–Dec 12th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Lizard-Flathead.

Forecast snowfall amounts have been upgraded and potential exists for a 'Fernie Effect' dump over Tuesday night. Increase ratings one step if we see more than 30 cm of new snow.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday night: Cloudy with increasing flurries bringing 15-25 cm of new snow. Moderate to strong southwest winds.Wednesday: A mix of sun and cloud with easing, isolated flurries and a trace of new snow. Strong west or northwest winds. Alpine high temperatures around -7.Thursday: Cloudy with another round of flurries bringing 2-4 cm of new snow. Strong to extreme southwest winds. Alpine high temperatures around -3 with freezing levels rising from 1500 to 2000 metres overnight.Friday: A mix of sun and cloud. Moderate to strong southwest winds. Alpine high temperatures increasing to around +1 as freezing levels rise to a possible 2300 metres.

Avalanche Summary

Preliminary reports from the Fernie area on Tuesday showed our new snow accumulations already producing small (size 1) wind slab releases with ski cutting on all aspects. Expect similar conditions on Wednesday but with an increased size and depth of slabs.The last notable avalanche was a size 2 human triggered avalanche on December 2nd in Cornice Bowl north of Fernie. It occurred on a northwest facing feature at 2300 m and ran on a crust layer. There are good photos in this MIN report.

Snowpack Summary

New snow has begin to bury the old surface that was noted earlier in the week for a cover of large, weak surface hoar crystals as well as hard wind slab and some sun crusts. Beneath the new snow and old surface, the snowpack has been stuck in early season conditions, hovering at roughly 100 cm of depth in alpine areas and much less at lower elevations. See the snow profile in our field team's MIN report for a visual representation of the snowpack here. Aside from storm slabs now building on the surface, a primary concern is the combination of weak facets and crusts in the bottom half of the snowpack. The crust is most prevalent at and above treeline and is likely most problematic on north-facing features, especially those that are large and planar in nature. A layer of large surface hoar can also be found at similar depths in some areas, as found in a recent MIN report here.

Problems

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.

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.