Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 6th, 2020–Dec 7th, 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, 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

Northwest Inland.

 Conditions may vary significantly from one slope to another. Avoid areas where recent snow has been drifted by wind and investigate deeper weak layers before committing to terrain. 

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

Sunday night: Mostly cloudy, scattered flurries with up to 5 cm of snow above 1200 m, moderate southwest winds, freezing level dropping to 1200 m.

Monday: Mostly cloudy, 5-10 cm of snow above 1200 m, moderate southwest winds, freezing level near 1200 m.

Tuesday: Partly cloudy, scattered flurries with up to 5 cm of snow, light to moderate southwest winds, freezing level dropping to 500 m.

Wednesday: Partly cloudy, light northwest winds, isolated flurries with trace accumulations, alpine high temperature -4 C.

Avalanche Summary

 During the weekend storm, professional operators reported small to large (size 1-2) natural and explosive-triggered wind slabs on northwest, north, and northeast aspects in immediate lee features. During peak warming, a widespread cycle of small loose wet avalanches was observed up to 1800 m. Shallow slabs in the new snow may be possible to trigger in wind-loaded steep, rocky, or convex features near ridge crests and roll-overs. See this MIN report for a great example. 

Outside of the region near Tatlatui Provincial Park on Friday, operators triggered two large (size 2) avalanches with explosives that released on weak snow at the ground. Earlier in the week, a series of very large (size 3-3.5) natural deep persistent slab avalanches were reported near Ningunsaw that also failed on weak snow at the ground. 

Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! 

 

Snowpack Summary

The weekend storm brought varying accumulations of snow followed by rain up to mountain top elevations. In many treeline and belowtreeline areas, the combination of above freezing temperatures and rain saturated the entire snowpack. As a result, snow has melted fast at lower elevations, and snowpack depths have seen rapid settlement. 

As the freezing level gradually drops below 1000 m by end of day Monday, a widespread melt-freeze crust will be left behind across aspects and elevations. Ongoing southwest winds are expected to drift 5-15 cm of new snow into wind slabs on lee and cross-loaded features in the alpine or in "alpine-like" features at treeline. Where snow accumulates over the recently formed melt-freeze crust, shallow slabs may be possible to trigger. 

In areas north and east in the region, the bottom half of the snowpack reportedly consists of weak snow interrupted by a crust from early November. These weak layers have produced very large deep persistent slab avalanches near the Ningunsaw and Tatlatui Provincial Parks. The extent of this snowpack structure in the region is not well-known. Smaller avalanches in the new snow may have the potential to step-down to deeper layers and to produce large, destructive avalanches. Large alpine slopes where the snow transitions from thick to thin are most suspect. 

Snowpack depths vary substantially with aspect, elevation, and wind exposure (check out this MIN report for a great visual). Lower elevation terrain may still be below the threshold for avalanches. 

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid freshly wind loaded terrain features.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.

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.