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Avalanche Forecast

Archived

Dec 8th, 2020–Dec 9th, 2020

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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

Reactive slabs may lurk on windloaded slopes and steep and convex features in the alpine. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

TUESDAY NIGHT: Isolated flurries, trace to 5 cm / Moderate to light west ridgetop wind / alpine low temperature -4 / Freezing level 1100 m

WEDNESDAY: Mostly cloudy, isolated flurries near the Coquihalla / Light to moderate southwest ridgetop wind / alpine high temperature -5 / Freezing level 1000 m

THURSDAY: Cloudy with sunny breaks / Light southwest ridgetop wind / alpine high temperature -2 / Freezing level 1200 m

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

Avalanche Summary

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

Around Whistler (which received more snow than the Duffy), storm slab avalanches to size 2 were triggered by explosives, and evidence of a natural avalanche cycle to size 2 was also reported.

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

Overnight Monday-Tuesday, rain and high freezing levels overnight produced a moist snowpack above 2000 m before freezing levels began falling. 

By Tuesday morning, 10-20 cm new snow accumulated above 1800m and the snow/rain line with moderate ridgetop winds. At upper (drier) elevations, the new snow covers a melt-freeze crust and old wind slabs. Dry snow accumulated around Cayoosh and the Duffy area, but sustained warm temps and rain saturated slopes around the Coquihalla.

A saturated snowpack is found at lower elevations, this will cool and freeze with falling temperatures.

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.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.