Avalanche Forecast
Issued: Dec 24th, 2019 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
cgarritty,
Avalanche Canada
Several weak layers are active in the snowpack, producing avalanches and concerning test results. Successfully managing this complex snowpack will be less about picking out the most problematic layer and more about choosing conservative terrain while the snowpack strengthens.
Summary
Confidence
Moderate -
Weather Forecast
Tuesday night: Cloudy with continuing isolated flurries and a trace of new snow. Light southwest winds.
Wednesday: Mainly cloudy with cloud decreasing late in the day. Light north winds. Alpine high temperatures around -8.
Thursday: A mix of sun and cloud with cloud increasing over the day. Light to moderate southwest winds increasing over the day. Alpine high temperatures around -7.
Friday: A mix of sun and cloud. Light to moderate west winds. Alpine high temperatures around -8.
Avalanche Summary
Several more large persistent slabs were triggered with explosives control in the Nelson area on Monday. These slabs featured crown depths of 15-120 cm, giving some evidence of wind loading. These avalanches are suspected to have released on our early November facet/crust layer, which exists below at least two other persistent weak layers of concern.
A widespread avalanche cycle occurred on Saturday, with observations of large artificially triggered avalanches continuing into Sunday. Many of these recent avalanches released within the storm snow, and large avalanches have been observed on all aspects and generally above 2000 m. Numerous other large to very large avalanches were also triggered by explosives on the late-November layer described in our Snowpack Summary.
Snowpack Summary
The past several stormy days saw around 70 to 100 cm of snow deposited in the region, initially accompanied by strong west wind. This snow has loaded multiple weak layers, including:
- a feathery surface hoar layer now buried around 70 to 110 cm.
- an older surface hoar layer buried about 90 to 130 cm, associated with a melt-freeze crust on steep south aspects.
- a complex layer of weak and sugary faceted snow, surface hoar, and melt-freeze crusts in the bottom half of the snowpack, buried in late November.
There is uncertainty on which of these layers will emerge as our primary persistent slab problem. However, given our extensive recent avalanche activity, it is prudent to expect that any one of these deeply buried layers could produce large and destructive avalanches with a human trigger.Â
Terrain and Travel
- Don't let the desire for deep powder pull you into high consequence terrain.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Make conservative terrain choices and avoid overhead hazard.
Problems
Persistent Slabs
Three different weak layers can be found in the snowpack, they are now deeply buried, and they have produced large avalanches as recently as Monday. It remains prudent to assume the layers are present and capable of forming very large, destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
Snowfall totals reached around 60 to 90 cm across the region from the weekend's storm. The snow fell with strong west wind, forming touchy slabs that have produced large and destructive avalanches. Storm slabs may remain reactive to skier traffic and may also step down to one or more weak layers that exist much deeper in the snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 25th, 2019 5:00PM
