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Avalanche Forecast

Archived

Feb 29th, 2020–Mar 1st, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

Wind-drifted snow at upper elevations is the primary concern for the region on Sunday. In the north, buried weak layers will require careful evaluation and terrain selection. Ice climbers be wary of periods of strong sun.

Confidence

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

Weather Forecast

Saturday night: Mostly clear, light northwest winds, freezing level dropping to valley bottom.

Sunday: Mostly clear, increasing cloud in the afternoon, light variable winds, freezing level 1000 m. 

Monday: Partly cloudy, isolated flurries with trace accumulations, moderate southwest winds, freezing level 1300 m.

Tuesday: Mix of sun and cloud, scattered flurries in the afternoon with up to 5 cm of accumulation, strong southwest winds, freezing level rising to 1500 m.

Avalanche Summary

No recent avalanches have been reported. Some minor snowballing was observed on steep, sunny slopes Wednesday and Thursday across the region. 

On Monday and Tuesday, several small to large (size 1-2) natural and human-triggered wind slab avalanches were observed on northeast, northwest, and west aspects in the alpine breaking 10-50 cm deep. 

Snowpack Summary

20-30 cm of snow has accumulated since Friday, with 30+cm in the south of the region (i.e. Coquihalla). Strong winds from the south switched to the northwest and decreased. The winds redistributed the storm snow into a complex pattern of reactive wind slabs on lee features at upper elevations and rapidly loaded cornices. Periods of sun on Sunday are expected to initiate pinwheeling and rollerballs from strong solar radiation on steep, sunny slopes. Ice climbers should monitor for the effect of solar radiation on overhead snow and for the potential for small loose wet avalanches to have consequences.

Buried 40-70 cm deep, a weak layer of sugary faceted snow and feathery surface hoar from February 22 may persist and warrants careful evaluation, particularly in the northern part of the region (i.e. Duffey/Hurley/Goldbridge). On south-facing slopes, this weak layer may be combined with a melt freeze crust. Check out the latest forecaster blog that offers a deeper dive into these conditions.

Also in the northern part of the region (i.e. Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced recent avalanche activity since February 12th. Rapid warming or heavy loading by new snow/wind/rain events has the potential to re-awaken this layer.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.