Avalanche Forecast

Issued: Dec 28th, 2021 4:00PM

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

Avalanche Canada shorton, Avalanche Canada

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Triggering avalanches is possible at treeline and alpine elevations. A tricky buried weak layer warrants careful terrain selection at these elevations.

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Confidence is due to a stable weather pattern; little change is expected for several days.

Weather Forecast

Cold arctic air will persist until Sunday.

TUESDAY NIGHT: Mostly clear skies, no precipitation, moderate wind from the north with gusts to 60 km/h, treeline temperatures around -15 C.

WEDNESDAY: Mostly sunny with some afternoon clouds, no precipitation, moderate wind from the north with gusts to 50 km/h, treeline temperatures around -15 C.

THURSDAY: Cloudy, light flurries with 5 cm of low density snow, light wind from the north, treeline temperatures around -12 C.

FRIDAY: Mostly sunny skies, moderate wind from the northeast with gusts to 50 km/h, treeline temperatures around -18 C.

Avalanche Summary

Small (size 1) wind slab avalanches were observed on south aspects on Monday as a result of reverse loading from northerly wind. There were also some small human triggered wind slabs over the weekend, including this one from Gin Peak that illustrates how recent wind patterns have left slabs in atypical locations.

We have been paying close attention to the persistent weak layer found in the region. The last reported avalanche on this layer was on Dec 24, but it produced several notable avalanches around Dec 16 at elevations between 1800-2100 m. While we have seen a decreasing trend in avalanche activity since then, the avalanche on the 24th provides a good indication of the type of terrain where this problem could persist. This size 2.5 skier-triggered avalanche occurred on a northwest facing slope around 2100 m in the Blackcomb backcountry, and propagated between some shallowly buried rocks.

Snowpack Summary

Northerly winds over the past few days heavily impacted the snow in open alpine terrain and left wind slabs in atypical locations. It may be possible to find 30 cm of low density snow in sheltered areas. 

A weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 100-200 cm). This layer has been most reactive at treeline and low alpine elevations, between 1800-2100 m. Although we have seen a decreasing trend in avalanche activity on this layer, it has still produced some notable human triggered avalanches over the past week. This problem is particularly hard to predict and poses a tricky low-probability high-consequence scenario (see the problem description and travel advice for suggestions).

Terrain and Travel

  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for areas of hard wind slab on alpine features.

Problems

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of facets above a crust that formed in early December is found 100-200 cm deep. While it has become less likely to trigger avalanches on this layer, the consequences are large. The most suspect terrain would be shallow rocky start zones at elevations between 1800-2100 m..

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2.5 - 3.5

Wind Slabs

An icon showing Wind Slabs

Shifting wind over the past few days has left wind slabs in unusual cross-loading and reverse-loading patterns. While these slabs may be difficult to trigger, their atypical spatial distribution could surprise riders.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 29th, 2021 4:00PM