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 16th, 2020–Dec 17th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Northwest Coastal.

Storm slabs will likely be reactive on Thursday even with a brief lull in between storms. They may step down to deeper weak layers initiating large to very large avalanches.

Confidence

Moderate - Uncertainty is due to limitations in the field data. Forecast snowfall amounts are uncertain.

Weather Forecast

A small break in the series of storms on Thursday before the next system arrives for the weekend.

Thursday: Snow amounts 10 cm. Alpine temperatures near -2 with the freezing level 700 m. Ridgetop wind 30-50 KM/hr.

Friday: Snow 15-25 cm accompanied by 35-75 km/hr southwest wind. Freezing level 800 m.

Saturday: Snow 20-30 cm and rising freezing levels to 1100 m. Ridgetop wind 25-80 km/hr from the southwest. 

Avalanche Summary

On Wednesday, On Tuesday a few small cornice failures were reported and an explosive triggered storm slab up to size 2. 

On Monday, a few naturally-triggered Icefall events up to size 2 were reported from Bear Pass. Loose-dry sluffing up to size 1 was seen from steep and rocky terrain features. The last deep persistent slab avalanches released on December 11 in the north of the region near Ningunsaw.

Data in this region is very sparse. Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter.

Snowpack Summary

By Wednesday morning the region received 25-35 cm of new storm snow with strong southwest wind. Expect reactive storm slabs particularly in wind-affected terrain at and above treeline. The snow will fall onto previous wind-affected snow at higher elevations, potentially a layer of surface hoar in sheltered areas, and a crust at lower elevations. Initially, the new storm snow will likely have a poor bond to these old snow surfaces.

The early-December crust is now down 100 cm in the alpine but close to the surface at and below treeline elevations. The early-November crust is buried around 100 to 200 cm at treeline elevations. The early-November crust may have weak and sugary faceted grains above it in parts of the region, which have produced large, full-depth avalanches in the past weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.

Terrain and Travel

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.