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Avalanche Forecast

Archived

Jan 6th, 2021–Jan 7th, 2021

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

Northwest Coastal.

Very conservative terrain choices are recommended as human triggered avalanches are likely and natural avalanches will continue at higher elevations.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

WEDNESDAY NIGHT: Scattered flurries continue with 5-10 cm of snow, strong southwest wind, treeline temperatures around -2 C.

THURSDAY: Scattered flurries throughout the day with 5-10 cm in most parts of the region but up to 20 cm along the coast, strong south wind, treeline temperatures around 0 C.

FRIDAY: Cloudy with a few sunny breaks, moderate southeast wind, treeline temperatures around -5 C.

SATURDAY: Cloudy with isolated flurries and up to 5 cm of snow, strong south wind, treeline temperatures around -3 C.

Avalanche Summary

Avalanche activity has been reported continuously since New Year's Day, with widespread natural size 2-3 storm slab avalanches at all elevations. Over this period there have been numerous reports from the Shames area of human triggered avalanches, including some very reactive storm slabs sitting above surface hoar and crust layers. Recent MIN reports show great photos of these avalanches, which at the time released on 30-70 cm deep weak layers. These layers should be roughly 100 cm deep now. Between Christmas and New Year's there were some notable snowmobile triggered avalanches on weak layers in the Nass/Sterling/Beaupre areas, and some very large explosive triggered avalanches on deep weak layers in the northern parts of the region.

As the storm eases off we are concerned about both the recently deposited storm slabs, and these buried weak layers (which vary throughout the region).

Snowpack Summary

A non-stop series of storms has deposited 75 to 150 cm of new snow since New Year's. The amount of snow, as well as the wind speed and direction, has been highly variable between different drainages over this period, so there is uncertainty about exactly what the upper snowpack will look like as we come out of this storm. However lingering storm and wind slabs will likely need a few days to stabilize.

Aside from this new snow, the main concerns vary throughout the region. In the Shames area, this new snow has been bonding poorly to a surface hoar and crust layer that is now an estimated 75-125 cm deep. A bit further north in the Nass/Sterling/Beaupre areas there is potentially still concern about an older weak layer of surface hoar and crust that is now roughly 150 cm deep. In the far north of the region there is concern about weak snow at the bottom of the snowpack. At this point there is some uncertainty about whether these layers will still be reactive after such an intense stormy period.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Make conservative terrain choices and avoid overhead hazard.
  • Stick to simple terrain or small features with limited consequence.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.