Avalanche danger is on the rise, especially in windy areas where 15 cm new snow accumulates by the end of Tuesday. The Monashees will probably have the highest snow amounts from Tuesday's storm.
Summary
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Monday Night: 2-5 cm new snow expected overnight.Tuesday: 10-20 cm new snow expected with increasing moderate or strong southwesterly winds. Freezing level around 600 m.Wednesday: Flurries. Moderate westerly winds. Freezing level around 1000 m.Thursday: Light snow, around 5 cm. Strong southwesterly winds. Freezing level rising to around 1400 m.
Avalanche Summary
During the upcoming stormy period, expect wind slab avalanches in exposed areas and loose dry avalanches in more sheltered locations.A MIN report from Saturday in the Keefer lake area describes a recent large (size 2) slab that released naturally from a steeper, open feature below treeline. The failure plane of the slab is uncertain but it suspected to be one of our mid-November surface hoar layers, possibly where it is combined with an underlying crust. The report also describes another snowmobile-triggered avalanche that occurred in the Kaslo area. Details on the incident are not complete but suggest that at least one individual was partly buried.
Snowpack Summary
10-20 cm of mostly low density new snow now rests on the previous snow surface. I expect this new snow to be initially poorly bonded, meaning the new snow will sluff readily in steep terrain. Lower in the snowpack, there is a lingering weak layer about 35-65 cm deep. This layer is comprised of weak, feathery surface hoar crystals that is most prominent at treeline, but may also be found in sheltered alpine areas. This layer has not been active recently, although there is some potential for it to awaken in response to new snow. If it was to come back to life, the most problematic places would be on south aspects at treeline, where the surface hoar formed above a sun crust.At the base of the snowpack is a crust that formed near the end of October. Concern for this layer is dwindling but it may still be worth considering in places such as steep, rocky, alpine terrain, especially where the snowpack is shallow. It would likely take a large trigger such as a cornice fall to produce an avalanche on this layer.
jfloyer,
Avalanche Canada
