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Archived

Avalanche Forecast

Dec 30th, 2020–Dec 31st, 2020
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Kootenay Boundary.

Concern remains for the persistent weak layers that exist in the top 80 cm of the snowpack. Persistent weak layers can be very difficult to manage, so a conservative approach to terrain is important.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy with scattered flurries, up to 5 cm / southwest wind, 20-30 km/h / alpine low temperature near -6 

THURSDAY - A mix of sun and cloud with isolated flurries / light northwest wind / alpine high temperature near -5 

FRIDAY -Flurries, 5-10 cm, with another 10-15 cm Friday night / southwest winds 25-50 km/h / alpine high temperature near -4

SATURDAY - Flurries, 5-10 cm, with another 15 cm Saturday night / southwest wind, 40-60 km/h / alpine high temperature near -2 / freezing level 1300 m

Avalanche Summary

There were a few size 1 storm slab avalanches reported near Big White on Wednesday.

There was one explosives triggered size 1 cornice avalanche reported near Rossland on Monday.

Many storm and persistent slab avalanches were observed last week. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and at elevations between 2000 and 2300 m. Although avalanche activity appears to have diminished, I wouldn't rule out the possibility of seeing more persistent slab avalanches.

Snowpack Summary

Stormy weather on Wednesday brought 5-10 cm of new snow and may have form new wind slabs in leeward terrain. 

Two weak layers are buried in close proximity to one another. They are 50-80 cm deep around Nelson and 30-50 cm deep around Rossland and other western parts of the region. The layers are composed of feathery surface hoar and sugary faceted grains and they overlie a hard melt-freeze crust. 

There was substantial avalanche activity on these layers prior to Christmas from natural and human triggers. Although reports of such avalanches have been dwindling, these weak layers remain a concern, as they can produce large and destructive avalanches.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Avalanche Problems

Persistent Slabs

Weak layers of surface hoar and/or faceted grains overlie a hard melt-freeze crust 30 to 80 cm deep. The new snow load before Christmas pushed this problem over the tipping point and resulted in large avalanches. Although the likelihood of triggering persistent slab avalanches is decreasing, the potential for triggering a high consequence avalanche should still be top of mind in your decision making process. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1.5 - 2.5

Wind Slabs

Watch for new snow and wind to form reactive slabs on leeward terrain in the alpine and near ridgetops.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1.5