Avalanche Forecast

Issued: Feb 27th, 2020 5:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

astclair, Avalanche Canada

Sea To Sky.

Anticipate increasing avalanche hazard as new snow accumulates and as winds increase. The incoming storm has potential to bring cornices and deeper weak layers to their tipping point. Conservative terrain use is warranted for Friday.

Summary

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

Thursday night: Cloudy, 5 to 10 cm of snow, moderate southwest wind, alpine temperature -3 C.

Friday: Cloudy, 5-15 cm of snow, southwest winds increasing to strong by end of day, freezing level 1300 m.

Saturday: Cloudy, 25-30 cm of snow, light southwest winds, freezing level 1000 m.

Sunday: Mostly clear, light southwest winds, freezing level 1000 m.

Avalanche Summary

On Wednesday, a large (size 2) human-triggered avalanche releasing on the February 22 surface hoar was reported. Small point releases in steep rocky south facing terrain around treeline have been recently observed.

Reports from earlier in the week include a natural storm and wind slab avalanche cycle up to size 2, primarily on northeast aspects in the alpine and upper treeline, releasing on the February 22 interface. This MIN post includes a photo of a skier triggered wind slab.

Snowpack Summary

By Friday afternoon, 15-25 cm of forecast snow is expected to form a new layer of concern. Strong winds from the southwest will likely drift the new snow into touchy wind slabs on lee features and bring cornices to their breaking point. Buried 40-70 cm deep, a weak layer of near surface facets facets or surface hoar from February 22 still lingers and has recently shown reactivity.

Faceted snow and crusts exist near the base of the snowpack in much of the region. This layer is has been dormant recently.

Terrain and Travel

Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
Minimize exposure during periods of heavy loading from new snow and wind.
Wind slabs are most reactive during their formation.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Wind Slabs

15-25 cm of new snow accompanied by strong southwest winds is likely to form fresh wind slabs on leeward terrain features at upper elevations. These areas of concern overlap with where cornices may also be reaching their breaking point.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A weak layer of near surface facets and surface hoar from February 22 will likely get buried down 40-70 cm. On solar aspects, these weak grains may be accompanied by a crust. As new snow and wind add to the slab above, there is growing concern for the size and likelihood of avalanches on this persistent weak layer.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Feb 28th, 2020 4:00PM