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Avalanche Forecast

Archived

Dec 15th, 2020–Dec 16th, 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 and human triggered avalanches likely.
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 avalanches possible, human triggered probable.

Regions

Northwest Coastal.

Another storm hits the region and storm slabs will likely be reactive, they may step down to deeper weak layers initiating large to very large avalanches. Avoid avalanche terrain during periods of heavy loading from new snow and strong winds. 

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to limitations in the field data.

Weather Forecast

An active weather pattern hits the region with fast-moving frontal systems bringing snow and strong wind through the forecast period.

Overnight Tuesday: Snow up to 25 cm with a strong southwest wind. Freezing level 700 m.

Wednesday: Another 10-25 cm of snow. Moderate and gusty southwest wind. Freezing level 800 m.

Thursday: Cloudy. Light snow 5 cm. Strong southwest wind.

Friday: Snow 20-30 cm. Strong southwest wind and freezing level 800 m.

Avalanche Summary

No new reports on Tuesday at the time of publishing.

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

The region will see substantial snowfall amounts Tuesday night and into Wednesday, especially to the south of the region as well as strong southwest wind. Expect storm slabs to build during the storm, 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

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Watch for fresh storm slabs building throughout the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • 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.