Avalanche Forecast

Archived

Feb 27th, 2020–Feb 28th, 2020

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast Inland.

Incoming snow and increasing wind are expected to complicate the existing wind slab problem. Caution around drifted slopes and roll-overs at upper elevations, especially where these slabs overly a weaker interface.

Confidence

Moderate - Uncertainty is due to the timing of the incoming weather system.

Weather Forecast

Thursday night: Cloudy, scattered flurries bringing a trace of new snow, moderate southwest winds, freezing level dropping below 1000 m.

Friday: Mix of sun and cloud, 5-10 cm of snow, moderate southwest winds with strong gusts, freezing level 1600 m in the north, 2000 m in the south.

Saturday: Cloudy, 10-15 cm of snow, winds decreasing and shifting from strong southwest to light northwest, freezing level 1200 m.

Sunday: Mostly clear, light variable winds, freezing level 1200 m.

Avalanche Summary

Some minor snowballing was reported on steep, sunny slopes Wednesday and Thursday across the region. On Monday and Tuesday, several small to large (size 1.5-2) 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

15-40 cm of recent storm snow (closer to 50 cm in the Coquihalla) has been redistributed onto lee features in exposed areas near and above tree line. This snow may overly isolated patches of surface hoar in sheltered areas or sun crusts on solar aspects, and it may remain possible to human trigger. Warming temperatures, 5-10 cm of new snow, and increasing southwest winds on Friday are expected to exacerbate this wind slab problem, especially where it overlies a weaker interface.

In the north part of the region (ie. Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced recent avalanche activity, with the most recent event on February 17. Rapid warming or heavy loading by new snow/wind/rain events has the potential to re-awaken this layer.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
Surface hoar distribution is highly variable. Avoid generalizing your observations.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.