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Avalanche Forecast

Jan 27th, 2020–Jan 28th, 2020
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
4: High
The avalanche danger rating below treeline will be high

Regions: Northwest Coastal.

Ongoing snowfall and wind are driving avalanche hazard. Seek out sheltered areas and dig down to investigate deeper layers before committing to terrain.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday night: Decreasing cloud, 2-5 cm of snow, light southwest winds, alpine temperature -3 C, freezing level dropping to 200 m.

Tuesday: Increasing cloud, 2-5 cm of snow, moderate south wind increasing to extreme overnight, alpine high temperature -2 C, freezing level rising to 500 m.

Wednesday: Mostly cloudy, 35-50 cm of snow, strong southwest winds with extreme gusts, alpine high temperature -1 C, freezing level rising to 800 m.

Thursday: Mostly cloudy, 30-40 cm of snow, strong south winds with extreme gusts, alpine high temperature -1 C, freezing level around 800 m. 

Avalanche Summary

Small pockets of human-triggered wind slab were recently reported at treeline elevations closer to Terrace, while larger (size 2-3.5) wind slabs were reported further north in the Bear Pass area releasing naturally from alpine start zones. Several of these avalanches released down to a weak layer formed in mid-January. During the weekend warm-up, numerous natural loose wet avalanches in steep terrain (size 1-2) were observed up to 1000 m. 

Reports of deep persistent slab avalanches have been trickling in throughout the month, with the last reported event occurring on Jan 17th. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. These have typically run in alpine terrain, on lee or cross-loaded slopes. Recent loading has been a good test for this layer and it seems to be trending less reactive.

Snowpack Summary

Ongoing snowfall and wind continue to build reactive slabs in lee and cross-loaded terrain features. Around 50-120 cm of storm snow over the past week is settling rapidly. The storm snow rests on a mix of extensively wind affected surfaces at upper elevations or a thick layer of weak facets. Recent avalanche activity in the Bear Pass area and snowpack tests results have indicated that this layer is still a concern. With more snow in the forecast later in the week, the reactivity of this layer will be important to track. Below tree line, a recent warm-up moistened snow surfaces up to 900 m, forming a temperature crust. This MIN report provides a helpful description of these conditions near Terrace. 

A crust from mid November lurks at the base of the snowpack. The last reported avalanche on this layer was Jan 17th, and it will most likely require a large trigger such as explosives or cornice fall to initiate this deep persistent slab problem.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Avalanche Problems

Wind Slabs

Strong southwest winds continue to drift new snow into wind slabs on lee features in the alpine and exposed ridges near treeline. While natural avalanche activity has tapered, human triggering may still be likely. The wind slab problem overlaps with areas where cornices are also a concern. 

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2.5

Persistent Slabs

A layer of weak, faceted snow from the previous cold snap is now buried 50-120 cm deep. This persistent weak layer will likely be more problematic in shallower areas in the region where slab depths are in the 40-80 cm range and where the facets may be more pronounced.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1.5 - 3