Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

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 possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Continued flurries with strong southwest winds are expected to create fresh wind slabs at upper elevations. Carefully evaluate conditions, avoid wind loaded areas, and seek out sheltered terrain for the best riding quality.

Confidence

Low - Uncertainty is due to the limited number of field observations. Forecast snowfall amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy with flurries, 5-10 cm, with up to 15 cm expected near Pine Pass / southwest wind, 40-60 km/h / alpine low temperature near -9

THURSDAY - Mainly cloudy with flurries, 5-10 cm / southwest wind, 30-50 km/h / alpine high temperature near -7

FRIDAY - Flurries, 10-15 cm / southwest wind, 60-80 km/h / alpine high temperature near -2 / freezing level 1500 m

SATURDAY - Flurries, 5-10 cm / southwest wind, 60-80 km/h / alpine high temperature near -3 / freezing level 1700 m

Avalanche Summary

There have been no recent avalanches reported in the region.

Snowpack Summary

10-25 cm of recent new snow sits on previously wind affected snow at higher elevations, and on a crust between about 1300-1600 m. Sheltered areas at treeline may now have 15-45 cm of soft snow on the surface. Moderate to strong southwest winds will likely redistribute the new snow, forming wind slabs in the alpine and in open areas at treeline.

A widespread crust layer that may have sugary faceted grains above it can be found near the bottom of the snowpack. Uncertainty remains about if and where this layer is a problem. Recent observations from the McBride area suggest the snow is well-bonded to this crust. Observations from around Tumbler ridge suggest ongoing concern for this layer in this zone. I suspect the layer to be potentially reactive in northern parts of the region, such as Pine Pass, but do not have observations to back this up.

Snow depths are approximately 150 cm around Pine Pass, Torpy and McBride and around 100 cm in the northeast around Tumbler Ridge.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.