Avalanche Forecast

Issued: Dec 17th, 2018 4:52PM

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

Avalanche Canada shorton, Avalanche Canada

HIGH danger ratings are based on the assumption the regions gets over 25 cm of snow by Tuesday afternoon.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

MONDAY NIGHT: 10-15 cm of snow as a front approaches, strong wind from the southwest, freezing level around 1300 m.TUESDAY: Heavy snowfall with accumulations of 15-20 cm, strong wind from the southwest, freezing level up to 1600 m.WEDNESDAY: Flurries easing throughout the day with localized accumulations of 5 cm, moderate wind from the southwest with strong gusts, freezing level drops to 1200 m, alpine high temperatures around -2 C.THURSDAY: The next system arrives late in the day, moderate wind from the west, alpine high temperatures around -2 C.

Avalanche Summary

Small loose dry avalanches (size 1) were observed in alpine terrain on Monday.On Saturday, a group of skiers remotely triggered a large (size 2) avalanche on a northeast facing slope at treeline in the Corbin area. The skiers were in dense trees and the avalanche released roughly 60 m above them. One skier was fully buried and the group successfully extricated them without significant injuries. For full MIN incident report follow this link.Large (size 2-3) natural avalanches were also reported at treeline elevations in the Harvey area on Saturday. Most of them were 30-40 cm deep storm slabs, but a few appeared to step down to deeper crust layers. See photos in this MIN report.

Snowpack Summary

Tuesday's storm will build fresh storm slabs, especially at higher elevations where strong wind will form extra thick slabs.The new snow is falling on moist snow below 1600 m and hard wind packed snow in the alpine. Roughly 30-50 cm of snow is settling above a weak layer composed of large surface hoar, facets, and/or sun crust. There have been numerous signs over the past few days that this layer remains weak (i.e. remote triggering from low angle terrain, wide propagations in avalanches), and the layer could become extra reactive with the additional load of the new snow on Tuesday.Several other weak layers have been observed in the lower snowpack such as early season crusts with weak facets. The most concerning crust is prevalent at higher elevations and is likely most problematic on north-facing features, especially those that are large and planar in nature.

Problems

Storm Slabs

An icon showing Storm Slabs
Storm slabs will grow throughout the day and be very reactive to human triggering. Natural avalanches are also likely if accumulations exceed 25 cm, especially on slopes being loaded by the wind.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Minimize exposure to avalanche terrain during periods of heavy loading from new snow, wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
A widespread weak layer is being stressed by the new snow and has the potential to produce large destructive avalanches.
Stick to simple terrain and be aware of what is above you at all times.Avoid areas with overhead hazard.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 2.5

Valid until: Dec 18th, 2018 2:00PM

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