Avalanche Forecast

Thursday night: Flurries, 5-15 cm. Alpine low temperature -9 C. Moderate gusting to extreme southwest wind. Freezing level to valley bottom.

Friday: Flurries and snow, 10-20 cm. Alpine high temperature -5 C. Moderate southwest wind gusting strong to extreme. Freezing level 800 m.

Saturday: Flurries, 5-15 cm. Alpine high temperature -8 C. Moderate west wind gusting to strong. Freezing level valley bottom.

Sunday: Mix of sun, cloud, and isolated flurries. Alpine high temperature -14 C. Light west wind occasionally gusting to moderate.

On Saturday, skiers triggered a small and stubborn size 1 wind slab in the immediate lee of a ridge crest. Limited visibility impacted observations, but we suspect touchy wind slabs were found in the alpine and treeline lee feature. Far to the east, a natural storm slab avalanche cycle size 1-2.5 was reported, most observed on southwest and northeast aspects between 1600-2000 m. 

Last weekend, several natural and human-triggered wind slab avalanches were reported (up to size 2.5). Reports indicate that recent storm and wind slab avalanches have failed on a faceted interface from mid-January that developed with cold temperature prior to the last heavy snowfall (see an example in this MIN report).

There have been reports trickling in over the past month of natural persistent slab avalanches up to size 3 in the Bulkley Valley. These are thought to have been failing on the November crust/facet layer near the ground. The last reported avalanches on this layer were Monday January 13th. Incremental snowfall and mild temperatures have likely promoted a decreasing trend in reactivity for this avalanche problem. 

Widespread slab development occurred with 10-25 cm storm snow accumulating with strong winds. Below the new snow, 25-70 cm of wind affected snow rests on mix of previously scoured surfaces or a weak layer of facets that developed in the mid-January arctic outflow event. At treeline, a suspect layer of surface hoar is found 1 m below the surface. Below treeline the new snow rests on a melt-freeze crust and a well settled snowpack.

A deep crust/facet layer lurks at the base of the snowpack and was responsible for couple of large avalanches earlier in January. While it is promising that last week's snowfall did not trigger avalanches on this deep persistent weak layer, there is lingering uncertainty as to whether this week's weather could meet the threshold. Triggering this layer is most likely from shallow, rocky start zones or with a large load such as cornice failure or rapid loading from snow and wind.

• Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
• Expect slab conditions to change drastically as you move into wind exposed terrain.
• Watch for avalanche hazard to increase throughout the day.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.