The Coquihalla will see reactive new storm slabs develop overnight. In the north of the region, light amounts of new snow coupled with strong winds will continue to stress deep weak layers which have recently produced very large avalanches.
Continued flurries and gusty winds will contribute to an ongoing storm slab problem. Expect to find the most reactive deposits in open areas and around ridge features at treeline and above.
Between Thursday and Saturday, in the northern part of the forecast region, weak layers at the bottom of the snowpack were stressed by the recent storm snow, and resulted in very large deep persistent slab avalanches failing naturally and from skier traffic. Two layers have been a concern in the north including a 100 cm deep surface hoar layer in sheltered areas around treeline and weak, facetted snow near the bottom of the snowpack in shallow rocky start zones at higher elevations. Ongoing loading from snow and wind will continue to stress weaknesses at the bottom of the snowpack.
Monday night: Scattered flurries bringing 20 cm to the Coquihalla, 5-10 cm elsewhere. Alpine low -6 C. Strong southwest wind. Freezing level 1100 m.
Tuesday: Flurries in the morning, clearing to sun and cloud. Alpine high -1 C. Light southwest winds. Freezing level rising to 1500 m.
Wednesday: Flurries bringing up to 5 cm new snow. Alpine high 0 C. Strong souyhwest winds, approaching extreme at ridgetop. Freezing level 1600 m.
Thursday: Mix of sun and cloud with flurries in the evening. Alpine high -3 C. Light to moderate southwest wind. Freezing level 1100 m in the north, 1500 m in the south.
Natural wind slab avalanches size 2-2.5 were observed on wind-loaded slopes in the alpine on Sunday.
Several very large (size 3) deep persistent avalanches were reported to have failed naturally between late Thursday and Saturday, the reports come from around the Duffey Lake area and further north in the region towards Gold Bridge and Whitecap Mountain. These avalanches occurred on east, north, and west aspects around 2000-2200 m.
On Friday, skiers remotely triggered a size 3 avalanche on a north aspect at 2100 m in the Duffey area and a size 1 deep persistent avalanche while traveling along a skin track on a west aspect at 2050 m near Whitecap Mountain.
30-50 cm of recent snow sits over the January 20 crust up to 2000 m. At upper elevations, this snow has been redistributed by recent strong southwest winds. Below 1600 m, overnight snowfall rests on a crust.
There have been two layers of concern in the northern half of the region (e.g. Duffey, Hurley). One is a weak layer of surface hoar buried about 100 cm deep in sheltered areas around treeline. The other is weak basal facet crust complex. The latter has been the failure plane in recently reported deep persistent avalanches and is most likely to be triggered in shallow rocky start zones. There are currently no concerns about deep weak layers in the south of the region (e.g. Coquihalla).
