Avalanche Forecast

Issued: Nov 26th, 2017 5:05PM

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

cgarritty, Avalanche Canada

Northwest Inland.

Avalanche danger will remain heightened while incremental loading continues to test the snowpack. Forecast winds are set to amplify storm slab danger at higher elevations.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

Monday: Cloudy with flurries bringing 5-15 cm of new snow, increasing overnight. Strong southwest winds. Alpine temperatures around -6.Tuesday: Mainly cloudy with flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds. Alpine temperatures around -6Wednesday: Mainly cloudy with isolated flurries bringing a trace to 5 cm of new snow, increasing over the day. Freezing level rising to 1300 metres with alpine temperatures around -3.

Avalanche Summary

One report from Wednesday describes several estimated Size 2.5-3 avalanches observed on the Kathlyn face of Hudson Bay Mountain. A recent report from social media showed a Size 2 avalanche that occurred last Monday in alpine terrain in the Babines. In spite of its age, the slide is notable for apparently having run on the late October persistent weak layer. No other new avalanches have been reported. Please post your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Snowpack depths over the south of the region are above average for late November, with total depths of approximately 150 cm present at treeline elevations and above. The past week of stormy weather delivered about 60 cm of new snow to form the upper snowpack in the region. A thin rain crust may exist at mid-depth within this new snow. Below the new snow, about 20-30 cm of settled storm snow lies above the widespread late October crust. This October crust is present near the base of the snowpack at all elevations and features a layer of weak, sugary grains above it. This "crust/facet combo" layer remains an ongoing concern for step-down potential from large triggers such as a storm slab release. This layer is less of a concern below treeline where it is broken up by vegetation near the ground.

Problems

Storm Slabs

New snow and wind inputs continue to promote storm slab formation. Expect slab formation to be more pronounced at higher elevations that see more wind effect.

Avoid steep convexities and areas with variable snow distribution.Watch for signs of instability such as whumpfing or cracking.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

The late October crust lies near the base of the snowpack and a layer of weak, sugary snow sits above it. This layer may react to a heavy trigger like a storm slab release. The first evidence of avalanche activity on this layer was recently reported.

Be aware of the potential for large avalanches due to weak layers at the base of the snowpack.If triggered, storm slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Nov 27th, 2017 2:00PM