Avalanche Forecast

Issued: Dec 15th, 2018 4:59PM

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

Avalanche Canada shorton, Avalanche Canada

Watch for unstable snow on steep and wind loaded terrain features.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SATURDAY NIGHT: Cloudy with clear periods, moderate wind from the south, alpine temperatures drop to -10 C.SUNDAY: Increasing cloud throughout the day, moderate wind from the southwest with strong gusts, alpine high temperatures around -2 C.MONDAY: Light flurries, strong wind from the southwest, freezing level rising to 1800 m.TUESDAY: 10-15 cm of snow, strong wind from the southwest, freezing level around 1800 m.

Avalanche Summary

Widespread natural avalanche activity was reported on Thursday and Friday, primarily size 1-2 wind slab avalanches on east-facing lee terrain in the alpine. Some appear to have stepped down to the deep persistent weak layer near the bottom of the snowpack. Heavy triggers, including, explosives, also produced some large and very large deep persistent slab avalanches (size 2-3) that failed on the weak snow at the bottom of the snowpack. These avalanches were primarily on north and east aspects and ranged in depth from 50-120 cm. On Thursday, the storm snow was also very reactive to skier and snowmobilie traffic, producing widespread cracking, whumpfing, and some small avalanches.See some photos of avalanche activity north of Crowsnest Pass from out field team's MIN report here.

Snowpack Summary

About 20-30 cm of new snow has buried previous snow surfaces that ranged from soft power to hard wind slab and sun crust. Strong winds have likely been aggressively forming wind slabs with the new snow at higher elevations.Beneath the new snow and old surface, the snowpack has a thin, weak structure, with the bottom half of the snowpack composed of weak facets and crusts. This basal layer has been reactive to heavy triggers, and terrain features like smooth alpine bowls with variable snowpack depths are suspect for human triggering.Currently only 30-100 cm of snow can be found in alpine areas and much less at lower elevations.

Problems

Wind Slabs

An icon showing Wind Slabs
Recent strong winds and new snow have set up wind slabs in many exposed alpine and treeline areas.
Be alert to conditions that change with elevation, aspect and exposure to wind.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
The weak snow in the lower snowpack could produce large avalanches. Be cautions in areas where the surface snow has formed a cohesive slab, such as around thick wind deposits.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.Be especially cautious as you transition into wind affected terrain.Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Dec 16th, 2018 2:00PM