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Archived

Avalanche Forecast

Feb 27th, 2020–Feb 28th, 2020
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
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
1: Low
The avalanche danger rating below treeline will be low
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
1: Low
The avalanche danger rating below treeline will be low

Regions: Kootenay Boundary.

Warming temperatures may exacerbate the strong over weak snow combination in the upper snowpack tomorrow. A conservative terrain use strategy is warranted to manage the uncertainty.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Thursday night: Partly cloudy, moderate southwest winds, freezing level 1500 m.

Friday: Mix of sun and cloud, moderate southwest winds increasing to strong by end of day, freezing level 2000 m.

Saturday: Mix of sun and cloud, up to 5 cm new snow, moderate southwest winds, freezing level 1400 m.

Sunday: Partly cloudy, light variable winds, freezing level 1400 m.

Avalanche Summary

Small wet loose activity was reported on steep, sunny slopes on Thursday. In a few cases, these initiated small slabs on the February 22 surface hoar. A large, natural avalanche on an east aspect at 2100 m was thought to have run on the February 22 surface hoar and stepped down to the February 13 surface hoar layer.

Since the weekend storm, numerous small (size 1-1.5) skier triggered avalanches have been reported on a variety of aspects above 1700 m. Avalanches attributed to the late February surface hoar layer have occurred primarily between 1900-2100 m. 

Snowpack Summary

20-35 cm cm of recent snow is settling over a layer of near surface facets or surface hoar in sheltered areas at all elevations. Warming temperatures and sun are speeding up settlement in the slab and promoting touchy conditions on this interface. In the alpine and exposed treeline, recent snow has been redistributed by strong west winds, loading deeper and more reactive deposits onto lee features. 

An older layer of surface hoar from mid-February now sits 50-80 cm deep. This weak layer produced significant avalanche activity focused in the east of the region prior to the last storm. While it is likely bonding over time, there is uncertainty around remnant reactivity. Shallower avalanches may have the potential to step-down to this layer. The remainder of the snowpack is well settled.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Stick to simple terrain or small features with limited consequence.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Avalanche Problems

Persistent Slabs

Warming temperatures and periods of sun are expected to promote cohesion in the recent snow over a lingering layer of buried surface hoar, making human-triggered avalanches likely. This problem will be more pronounced where the wind has drifted the recent snow near tree line. Although less likely, a melt freeze crust buried down 60-80 cm may also become more reactive as a persistent weak layer with warming temperatures. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2