Avalanche Forecast

Issued: Feb 15th, 2020 4:00PM

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

Avalanche Canada cgarritty, Avalanche Canada

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Start small and aim for areas that haven't been exposed to recent winds. The possibility for large persistent slab avalanches from suspect terrain features should continue to figure into your terrain decisions.

Summary

Confidence

Moderate -

Weather Forecast

Saturday night: Cloudy with easing flurries bringing about 5 cm of new snow. Moderate to strong west winds, easing into the morning.

Sunday: Cloudy with scattered convective flurries giving a trace to 10 cm of new snow. Light southwest winds shifting northwest and increasing. Alpine high temperatures around -11.

Monday: Mainly cloudy. Light to moderate west winds, easing over the day. Alpine high temperatures around -9.

Tuesday: Mainly sunny. Light southwest winds. Alpine high temperatures around -4.

Avalanche Summary

Reports from Friday included an observation of a large cornice-triggered wind slab in Morning Bowl - see the report here. Ski cutting also produced small storm slab releases on steep rolls below treeline. No new persistent slab releases have been reported, but recent activity on deep weak layers suggests the possibility for this type of activity should still figure into terrain selection decisions.

Reports from Thursday's storm showed an uptick in avalanche activity brought on by new snow and wind. Observations were limited, but one large (size 2) natural wind slab was reported in the Kispiox area while more numerous dry loose releases and larger audible avalanches were seen and heard further west in the Howsons. More widespread natural storm slab activity was observed in our neighbouring Northwest Coastal region.

During the first half of the month there were many very large and destructive avalanches failing on deeply buried surface hoar and crust/facet layers near the bottom of the snowpack. The bulk of this activity occurred above treeline on north through east facing aspects, but large alpine slopes that have not yet avalanched should be treated as suspect. A few examples of the most recent activity are reported here:

Feb 11: Large (size 2.5) avalanche triggered by a large snow machine in the Kispiox area.

Feb 9: Very large avalanche on the Kathlyn Face near Smithers. Details/Photos here and here.

Feb 9: Large avalanche in the French Peak Complex. Details/Photos here.

Feb 9: Very large avalanche near the Pine Creek Trail. Details/Photos here.

Feb 8: Large snowmobile triggered avalanche in the Babines. Details/Photos here.

Feb 8: Very large avalanche on Mt. Elmstead above Silver King Basin Trail in the Babines. Details/Photos here.

Snowpack Summary

A variable trace to 20 cm of new snow accumulated in the region over Friday night and Saturday, bringing snow totals for the week to roughly 10-40 cm. The greatest accumulations can be found in the west of the region. 

With consistently elevated recent winds, each layer of recent snow has buried mainly wind-affected surfaces in exposed areas before subsequently being redistributed and affected by wind itself. In more sheltered areas, the recent snow collectively overlies crusts that can be found up to roughly 1200 m as well as on open south-facing slopes.

A weak layer of faceted snow that formed during cold weather in mid January is buried approximately 60-120 cm below the surface. Depending on location this layer may be composed of soft facets, surface hoar, or both. As a product of previous widespread cold temperatures, the faceted snow associated with this layer exists all over the region, however it may be bridged over by a firm crust at lower elevations. A few large avalanches were triggered on this layer in the first half of the month.

An older Crust/facet layer from November, lurking at the base of the snowpack, produced many very large avalanches during the first half of the month. As a product of old, weak snow from the early season, this layer is most likely to be found at high elevations.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

Wind Slabs

An icon showing Wind Slabs

Consistent recent light snowfall and strong westerly winds have formed wind slabs in exposed areas - especially in the immediate lee of ridge features. Avalanches in surface layers around steep, rocky features at ridgecrest may carry the risk of triggering a deeper weak layer. 

Steep sheltered slopes at lower elevations may still be capable of producing storm slab releases with a trigger, particularly in parts of the region with 30 or more cm of recent snow.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

A concerning number of large, deep and destructive avalanches have been human triggered and have ran naturally on deeply buried weak layers in the last two weeks. Large alpine features that have not yet slid need to be treated as suspect, especially if they have seen significant recent wind loading. Wind slab or cornice releases are likely triggers for this problem. Human triggering is most likely in shallow, rocky areas where the snowpack transitions from thick to thin.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2.5 - 3.5

Valid until: Feb 16th, 2020 5:00PM

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