Avalanche Forecast

Issued: Dec 9th, 2020 4:00PM

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

Avalanche Canada dsaly, Avalanche Canada

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Keep a lookout for any lurking slabs in steep and convex features with dry snow.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

WEDNESDAY NIGHT: Mostly cloudy / Light to moderate southwest ridgetop wind / alpine high temperature -5 / Freezing level dropping to valley bottom

THURSDAY: Cloudy with sunny breaks / Light southeast ridgetop wind / alpine high temperature -46/ Freezing level 800 m

FRIDAY: Sun and cloud / Light southwest ridgetop wind / alpine high temperature -6 / Freezing level 800 m

SATURDAY: Sunny / Light southwest ridgetop wind / alpine high temperature -5 / Freezing level valley bottom

Avalanche Summary

Evidence of a widespread natural storm slab (size 2-3) and wet avalanche (size 1-2) cycle was reported Tuesday in the mountains north of Pemberton.

Loose wet and wet slab avalanches to size 2 and glide crack releases were observed around the Coquihalla Tuesday, these were triggered by heavy rain and high freezing level.

On Monday afternoon around the Duffy, small size 1 loose-snow and low density slab avalanches failed naturally and with skier traffic as snow began to accumulate and load ridgetops. Small loose wet avalanches were observed below 1600 m.

A notable observation in the Duffy Area: On Tuesday Dec 1, a large size 3 natural avalanche was observed on a NE aspect at 2400 m. It was reported as a cornice failure triggering the slope below and appeared to have slid on the early November crust near the base of the snowpack.

Have you been out and about in the mountains? If so please submit to the Mountain Information Network (MIN). It doesn't have to be technical it can be as simple as a photo. Photos are especially helpful! Sending out a big thank you to the already submitted MIN's this season. Thanks everyone!

Snowpack Summary

Early this week, rain and high freezing levels produced a moist snowpack above 2000 m. As freezing levels fell, 10-20 cm new snow accumulated above 1800m and the snow/rain line with moderate ridgetop winds. 

A dusting of flurries covers a melt-freeze crust upwards of 2000 m. Above 1800-2000 m, recent flurries cover the settling and drying storm snow, over a variety of older crusts and wind-affected surfaces.

Below 1800 m and where rain achieved full saturation, the snowpack is uniform. At higher elevations, the lower snowpack is characterized by a few crusts that formed during warm periods in November. 

  • In the north, treeline snowpack depth sits around 80 to 150 cm, and decreases rapidly below 1600 m. The crust of note here is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. We have a lot of uncertainty on the reactivity of this layer - we're keeping it on our radar because we don't have enough information. Recent snowpack tests in the Cayoosh zone found this layer present and down 60 cm, and unreactive to snowpack tests. 
  • In the south of the region, treeline snowpack depth sits around 70-120 cm. The deeper crusts in this area are generally down around 60-80 cm in the alpine and well bonded to surrounding snow.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation and wind exposure.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.

Problems

Wind Slabs

An icon showing Wind Slabs

Storm snow reactivity is decreasing. Keep a look out for lingering slabs around steep rolls and extreme terrain.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 1.5

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

In the north of the region (e.g., Duffey Lake), a weak layer of sugary faceted grains around a hard melt-freeze crust sits near the base of the snowpack. There is a lot of uncertainty on the reactivity of this layer - we're keeping it on our radar because we don't have enough information. Be wary of overhead hazards, a large impact (like a cornice failure - see avalanche summary) could trigger the slope below. Keep in mind if this layer is triggered, it will likely produce large avalanches. This problem does not exist in the south of the region.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

1.5 - 2.5

Valid until: Dec 10th, 2020 4:00PM