Avalanche Forecast

Issued: Dec 6th, 2017 4:33PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is low. Known problems include Wind Slabs, Loose Wet and Deep Persistent Slabs.

cgarritty, Avalanche Canada

Northwest Coastal.

Warm, sunny conditions will increase the range of avalanche problems as well as their potential for reactivity.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Thursday: Mainly sunny with some valley cloud due to an alpine temperature inversion. Light south winds. Freezing level to 3200 metres with alpine temperatures of +8. Cooler temperatures at lower elevations.Friday: A mix of sun and cloud, cloud increasing over the day. Strong south winds. Freezing level dropping from 2400 to 2000 metres over the day with alpine temperatures from +5 dropping to around 0 as the temperature inversion breaks down.Saturday: Cloudy with scattered wet flurries bringing approximately 5 cm of new snow to the alpine. Rain below about 1000 metres. Moderate south winds. Freezing level to about 1500 metres with alpine temperatures around 0.

Avalanche Summary

Reports from the Bear Pass area on Monday showed isolated wind slabs releasing naturally to Size 2 from steep, north-facing alpine features. Looking forward to the warming that is forecast for the next couple of days, keep in mind that the strength of the bond between our recent storm snow and deeper buried crusts remains in question (especially at the basal crust). The possibility for failures at these deep interfaces will be higher while temperatures remain unseasonably warm. For the near term, it is recommended to take a conservative approach to route selection by traveling through low consequence terrain.

Snowpack Summary

Snowpack depths in the region range from approximately 140 to 190 cm at treeline elevations. Recent strong winds (mainly southwest) have redistributed surface snow into deep deposits of wind slab on leeward slopes. A layer of large surface hoar that was recently observed in the Shames area is now buried about 15 cm below the surface. Information on the distribution and reactivity of this layer is limited. Below it, storm snow received over last week is gradually settling above a 5-10 cm thick crust (November 23) down roughly 70-100cm. Another layer of surface hoar (November 11) continues to be observed down approximately 140 cm in the Bear Pass area, showing some signs of improved bonding. The widespread crust/facet interface that was buried at the end of October can now be found 90-160 cm deep. Below it, the basal snowpack is a mix of weaker, sugary snow. Both the late October crust and basal snowpack remain ongoing concerns as they continue to produce hard but sudden snowpack test results.

Problems

Wind Slabs

Strong south to west winds have blown our recent snow into wind slabs in lee terrain at higher elevations. Thursday's warm temperatures will promote natural releases from steep terrain and may make slabs more reactive to rider triggers.

Use ridges or ribs to avoid pockets of wind loaded snow.Avoid steep convexities or areas with a thin or variable snowpack.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Loose Wet

Warm, sun-exposed slopes could produce wet loose avalanches either naturally or with rider triggers on Thursday, especially in steeper terrain.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

Uncertainty still exists around the reactivity of layers sitting near the base of the snowpack. Conservative terrain selection is warranted while the snowpack reacts to the current warming pattern. Shallow releases may step down to deep weaknesses.

If triggered, storm/wind slabs may step down to deeper layers and result in large avalanches.Minimize your exposure to areas with overhead hazard.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Dec 7th, 2017 2:00PM