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Avalanche Forecast

Archived

Jan 6th, 2019–Jan 7th, 2019

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

Regions

Northwest Coastal.

New snow has been accumulating at upper elevations over the past few days. Expect to see new wind slab formation as forecast winds redistribute the new snow.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY NIGHT: Cloudy with flurries, moderate west winds, alpine temperature -10 CMONDAY: Cloudy with sunny periods, moderate west winds, alpine temperature -7 CTUESDAY: Cloudy with sunny periods, Light to moderate east winds, alpine temperature -6 CWEDNESDAY: Flurries with 5-10 cm accumulation, moderate southeast winds, alpine temperature -8 C

Avalanche Summary

The most recent reports of avalanche activity were from last Thursday; small (size 1) wind slabs were triggered by skiers in wind-loaded terrain features.A natural avalanche cycle occurred during the storm from last Monday to Wednesday, with many large to very large avalanches (size 2 to 3.5) propagating widely and running far. For example, see the MIN reports here and here.

Snowpack Summary

The surface snow consists of about 10-20 cm of new snow in the Terrace area. The upper snowpack varies substantially with elevation. Above around 1400 m, expect to find lingering wind slabs from last Tuesday's storm, which dropped upwards of 100 cm of snow with strong southwest winds. Below around 1400 m, the storm began with snow and switched to rain and may have switched back to snow again. It is likely that the wet snow has now frozen into a thick and supportive melt-freeze crust.In the northern part of the region around Ningunsaw pass, all this snow may overly a couple weak layers of feathery surface hoar buried near the end of December. Expect to find these layers about 50 to 120 cm deep.For most of the region around 150 to 200 cm deep, a weak layer of sugary faceted snow buried on December 8 may still exist. It is likely that this layer was the culprit of a large, remotely-triggered avalanche on December 30 near Terrace, described in a MIN report here. The likelihood of triggering this layer is decreasing, but it could be triggered by humans in shallow snowpack areas.

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.