Avalanche Forecast

Issued: Dec 10th, 2021 4:00PM

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

Mark Herbison,

Glacier.

New snow with strong winds will drive up the avalanche danger on Saturday.

Expect rapid storm slab development in loaded areas and fast sluffing in steep, sheltered terrain.

Travel in avalanche terrain is not recommended.

Summary

Weather Forecast

A Pacific 'Party' Front will arrive late this evening, bringing 15-30cm of new snow and 50-80km/hr South West winds along for the ride. Temps to remain cool throughout the storm. Sunday will see another 5-10cm of snow and 20-50km/hr Southerly winds with another pulse of snow arriving on Tuesday.

Snowpack Summary

45cm of storm snow since Wednesday, with 20-40km/hr Southerly winds creating fresh slabs in exposed terrain features and loose dry avalanches in steep sheltered terrain. The Dec 1st rain crust is ~15cm thick at 1900m, buried ~70cm down and can be found up to 2300m. The mid and lower snowpack is generally rounded, well bonded and strong.

Avalanche Summary

Avalanche activity will increase throughout the day on Saturday.

Numerous reports on Friday of size 1 skier triggered wind/soft slab avalanches in steep terrain and on convex rolls.

Several natural avalanches from the steep terrain on Mt. Tupper up to size 2.5.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

Problems

Storm Slabs

Forecasts vary on snow amounts, but we can expect ~15-30cm of new snow by Saturday afternoon with 50-80km/hr South West winds. Expect fast sluffing in steep terrain and avoid wind loaded areas where the storm slab will be the deepest.

Storm snow is forming reactive slabs.
Avoid avalanche terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Persistent Slabs

50-90cm on the Dec 1 crust, which is beginning to gain enough cohesion to fail as a slab where the interface bond is weak. The incoming storm may be enough to wake this problem up. It is mainly an issue at treeline, but extends into the lower alpine.

Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.
If triggered, the storm slab may step down to the persistent layer, resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Dec 11th, 2021 4:00PM