Avalanche Forecast

Issued: Feb 12th, 2020 4:00PM

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

Avalanche Canada cgarritty, Avalanche Canada

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A complex and dangerous snowpack has taken shape in our region, and a strong storm on Thursday won't improve matters. Forecast snowfall varies widely over the region, so make observations as you travel and expect stability to deteriorate over the day.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: Cloudy with flurries bringing 10-15 cm of new snow. Extreme southwest winds.

Thursday: Cloudy with continuing flurries bringing about 10 cm of new snow, continuing overnight. Moderate to strong southwest winds shifting west. Alpine high temperatures around -11.

Friday: Overcast, freezing level around 600 m, strong to extreme southwest wind, 1 to 5 cm of snow possible. Alpine high temperatures around -11

Saturday: Cloudy with continuing light flurries bringing up to 5 cm of new snow, easing overnight. Moderate southwest winds, easing overnight. Alpine high temperatures around -9.

Avalanche Summary

Another recent large (size 2.5) persistent slab avalanche, triggered by a large snow machine, was observed in the Kispiox area on Tuesday, this time failing on a southeast-facing slope at about 1600 metres.

Since February 3rd there have been many very large and destructive avalanches failing on deeply buried surface hoar and crust/facet layers at the bottom of the snowpack. The bulk of the activity has been above treeline on north through east facing aspects, but all alpine slopes that have not yet avalanched need to be treated as suspect. A few examples of the most recent activity are reported here:

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.

Persistent slabs are not the only problem either, over the weekend and into Monday some touchy wind slabs were observed, check out a MIN submission here that is a great example of this kind of activity. 

Looking forward, forecast new snow and wind will further strain persistent weak layers while adding to wind slab problems on Thursday.

Snowpack Summary

Open terrain continues to be heavily affected by strong wind from the west which has been actively loading lee terrain features and seems to be pushing the persistent slab problem to it's breaking point. Crusts can be found on the surface up to roughly 1200 m and on open south-facing slopes. 

Weak layers formed during cold weather in January may be part of the mechanism that has been producing the recent rash of very large avalanches. Depending on location these layers may be composed of soft facets or surface hoar and are typically buried 60-120 cm below the surface. 

Crust/facet layers that lurk at the base of the snowpack have reactivated and have consistently been producing very large avalanches since February 3rd. The most recent signs of instability with these deeper layers have been around Smithers, Hazelton, the Kispiox and the Babines, but persistent weak layers could be a problem on slopes anywhere in the region. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Avoid lingering or regrouping in runout zones.

Problems

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Many very large, deep and destructive avalanches have been human triggered and have ran naturally since February 3rd. As visibility improves and the days grow longer there is a natural tendency to push into new terrain, but we need to recognize that places that haven't seen a lot of traffic may actually be more likely to produce these monster avalanches than places with lots of tracks. Regardless, any alpine feature that has not yet slid needs to be treated as suspect. The frequency of these avalanches seems to be picking up and this problem isn't expected to go away anytime soon.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2.5 - 4

Wind Slabs

An icon showing Wind Slabs

Watch for the formation of fresh wind slabs on Thursday as light snowfall combines with strong to extreme southwest winds.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2

Valid until: Feb 13th, 2020 5:00PM