Avalanche Forecast

Issued: Dec 11th, 2018 5:08PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs and Deep Persistent Slabs.

cgarritty, Avalanche Canada

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.

Summary

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

A dump of snow over Tuesday night will combine with forecast strong winds to form reactive new storm slabs. Storm slabs have the potential to produce very large avalanches if they step down to the weak snow in the lower snowpack.

Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with elevation, aspect and exposure to wind.If triggered, storm slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

The weak structure of our snowpack will be tested by a new load of snow - and even more so by any storm slab avalanches. Triggering a deep weakness would produce a large avalanche. Be especially cautious in alpine areas that form deep wind deposits.

Be especially cautious as you transition into wind affected terrain.Avoid shallow, rocky areas where the snowpack transitions from thick to thin.Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 12th, 2018 2:00PM