Avalanche Forecast

Moderate -

Friday: Clear. Light to moderate east winds.

Saturday: Sunny. Moderate to strong east winds. Alpine high temperatures around -16.

Sunday: A mix of sun and cloud. Light variable winds. Alpine high temperatures around -16.

Monday: Cloudy with isolated flurries and a trace to 5 cm of new snow. Light to moderate southwest winds shifting northwest. Alpine high temperatures around -13.

A bout of sustained strong easterly winds prompted widespread wind slab formation and reactivity on Friday. Many 20-50 cm-deep slabs released naturally, with skier triggering and with explosives on Friday, some with remarkably wide propagation. Expect this reactivity to persist through the weekend.

We also have many recent reports of persistent slab avalanches triggered by skiers at elevations around treeline (1800-2000 m) where our active persistent weak layer exists as surface hoar. Check out the MIN for more details - there's a lot to see.

Another explosives-triggered persistent slab in the Bonningtons on Tuesday stepped down to our early December crust layer to produce a 200 cm-deep, size 3.5 (very large!) avalanche. A similar avalanche (size 3.5, step down to December crust) occurred naturally in the same area in the first week of February.

Snow from the past week has seen a great deal of wind effect at upper elevations and may contain a freezing rain crust or surface hoar at lower elevations. It continues to settle over a weak layer buried 60-80 cm deep. 

This persistent weak layer may exist as facets or a crust but it has been most reactive where it exists as large surface hoar crystals in sheltered areas treeline and below. Surface hoar has potential to surprise backcountry users with how widely the fracture can travel across slopes. This layer is slow to gain strength and requires careful terrain selection, even as its likelihood of triggering gradually diminishes.

There are several more layers of surface hoar in the mid snowpack, with the most notable one down about 80-120 cm. This layer was buried in early January. These older layers may take precedence over the layer described above in shallower snowpack areas from the Nelson Range through to the Okanagan.

A crust surrounded by weak faceted grains is buried deep within the snowpack. It may be possible to trigger this layer with a large load in a shallow rocky start zone.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.