Recently touchy storm slabs are expected to remain reactive to human triggering on Sunday. A persistent weakness in the snowpack has also recently resulted in some very large avalanches. Conservative terrain selection remains critical.
Summary
Confidence
Moderate - Due to the number of field observations on Saturday
Weather Forecast
Mostly cloudy conditions are expected on Sunday with the possibility of light flurries. Alpine wind is expected to be moderate from the south and afternoon freezing levels are forecast to be around 1000 m. A mix of sun and cloud is forecast for Monday and Tuesday with periods of light flurries possible. Alpine winds are expected to be mainly light and afternoon freezing levels are forecast to be between 500 and 1000 metres.
Avalanche Summary
On Friday, a natural size 3 storm slab avalanche was observed on a west aspect at 2500 m in the northern Monashees. This occurred on a convex glacial feature and the slab was 80 cm thick. An avalanche accident was reported in the Allen Creek riding area and up to 6 people may have been buried but details are still limited. Three large remotely triggered avalanches were also reported on Friday. Two of these were expected to have released on the mid-January layer below the recent storm snow. The third released on mid-December layer down around 80 cm and was triggered from 100 m away. Explosives triggered four persistent slab avalanches size 2.5-3 which are expected to have released on the mid-December layer down around 1.5 m. On Sunday, the recent storm snow is expected to remain reactive to human triggering in wind loaded terrain and steep unsupported or convex features. The mid-December weak layer is a real concern for the region and persistent slab avalanches remain possible. It may be possible to trigger this layer in shallow snowpack areas and smaller storm slab avalanches could step down to this layer in all areas.
Snowpack Summary
40-60 cm of recent storm snow typically overlies the variable mid-January interface which consists wind affected surfaces in exposed terrain, surface hoar up to 7 mm in sheltered areas, and/or widespread faceted old snow. Strong southwest winds during the storm have redistributed the new snow and developed wind slabs in leeward terrain features. In deeper snowpack parts of the region, the mid-December facet layer typically lies around 1.5 m below the surface. In shallower areas, particularly those in the southeast (Allen Creek), North (Sugar Bowl) and likely some western areas around Quesnel and Barkerville, the snowpack is likely a lot more suspect, with a thicker, more pronounced facet layer buried only 50-60 cm below the surface.
rbuhler,
Avalanche Canada
