Recent snow and strong winds in the alpine and treeline Friday night have formed deep pockets of touchy storm slab. Caution solar triggering of the new snow when the sun comes out Saturday morning.
The added stress and slab character of the new snow load may increase the reactivity of the layer, which is now buried 50-100 cm deep. Human triggering of weak layers at this depth is definitely possible and would result in large, high consequence avalanches.
40-60 cm of new snow followed by strong to extreme winds Friday night have likely formed deep pockets of storm slab in lee features in the alpine and treeline. The new snow will be sensitive to triggering when the sun comes out on Saturday.
Friday night: Heavy snowfall tapering overnight accumulating 10-15 cm. Wind increasing to strong southwest, approaching extreme at ridgetop. Alpine low temperature around -12 C. Freezing levels rising to 1000 m by 10 pm, then back down to valley bottom overnight.
Saturday: Sunny in the morning, cloud increasing in the pm, moderate southwest wind, alpine high temperatures around -9 C.
Sunday: Mix of sun and cloud with isolated flurries accumulating up to 5 cm, light to moderate west wind, alpine high temperatures around -7 C.
Monday: Mix of sun and cloud with isolated flurries accumulating up to 5 cm, strong southwest wind, alpine high temperatures around -7 C.
A widespread avalanche cycle up to size 3 was reported from the Howson range during the storm on Friday. This cycle is likely to be ongoing throughout the southern part of the region where more than 40 cm of snow fell on Friday.
Before the storm, reports of persistent slab avalanches associated with buried surface hoar were trickling in, from Ashman, Telkwa and Howson areas. They included natural and artificially triggered avalanches ranging in size from 1.5-3, and have occurred on all aspects mainly at treeline but also in the alpine. The new snow load will increase the size and consequences of avalanches on these layers.
40-60 cm of new snow from the past 36 hours has been highly wind affected overnight by strong to extreme winds. Expect to find deep wind loaded pockets below ridgetops and the lee sides of features all the way down to treeline. Below treeline, soft snow will be found down at least as far as 1000 m, where freezing levels may have creeped up to overnight.
A couple of layers of surface hoar are now buried 50-100 cm below the surface in sheltered areas around treeline. Reports of avalanche activity on these layers suggest they have recently become active, and the new snow load will provide additional stress.
