Avalanche Forecast

Archived

Dec 4th, 2020–Dec 5th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast Inland.

Above freezing temperatures up high over night and into the day Saturday will continue to stress the snowpack. Consecutive hot days are increasing the likelihood of triggering large avalanches on a crust near the bottom of the snowpack.

Confidence

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

Weather Forecast

FRIDAY NIGHT: Clear / Moderate, southwest ridgetop wind / alpine low temperature 0 / Freezing level 3000 m.

SATURDAY: Sunny / Moderate, south ridgetop wind / alpine high temperature +6 / Freezing level dropping gradually to 2000 m.

SUNDAY: Mix of sun and cloud / Moderate, southwest ridgetop wind / alpine high temperature -3 / Freezing level 1000 m.

MONDAY: Cloudy with flurries; 0-3 cm. / Strong, southwest ridgetop wind / alpine high temperature 0 / Freezing level rising to 2000 m.

Avalanche Summary

No new avalanche observations submitted on Thursday.

On Wednesday, the northern part of the region, several natural avalanches were reported up to size 2 with some older ones from the previous storm up to size 2.5. A couple of isolated natural glide crack avalanches up to size 1.5 were also reported. In the southern half, numerous natural wet loose avalanches occurred up to size 2 mostly from southerly aspects.

On Tuesday, 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.

As warm air and sunshine hit the region again Friday and Saturday I expect natural avalanche activity to occur. The longer the heat sticks around the deeper it drives into the snowpack potentially initiating larger avalanches.

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

Recent sun and warm air well into the alpine had the greatest impact on the upper snowpack, showing signs of instability and promoting further slab development and cohesion. This may be most concerning where these slabs sit above an old thin crust on south aspects and feathery surface hoar crystals in wind-sheltered areas. New surface hoar formation can be found on slopes where it was protected from the warm temperatures, sunshine and wind. Northerly aspects will likely see fresh wind slab development at upper elevations on leeward slopes and melt-freeze conditions may exist on most aspects and elevations.

The lower snowpack is characterized by a few crusts formed during warm periods over the last month.

In the north, treeline snowpack depth sits around 80 to 120 cm. The crust of note here is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. Snowpack tests and recent avalanche activity suggest that this layer could be triggered by humans and produce large avalanches.
In the south of the region, the snow line has been reported around 700 m near Hope, and treeline snowpack depth sits around 80-150 cm. Melt-freeze snow surfaces likely exist after the rapid warming on Wednesday. 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

Avoid exposure to overhead hazards when solar radiation is strong.
Back off slopes as the surface becomes moist or wet with rising temperatures.
If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

Problems

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.