Northwest Coastal

Persistent weak layers are slow to heal, and they may continue to be reactive when the new storm snow arrives on Friday.

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Friday

Cloud developing overnight combined with moderate to strong northerly winds. Increasing cloud during the day on Thursday with moderate north winds and a chance of flurries. The recent temperature inversion should deteriorate as the Low pressure system moves down the coast from the north. Expect alpine temperatures around -7. Snow developing overnight into Friday, expect 5-10 cm by morning and another 10-15 cm during the day. Continued snow is forecast for Saturday, at this time it looks like another 5-10 cm by morning.

On Tuesday, a size 2.0 persistent slab was released by explosives control in the Shames area that was 40-60 cm deep on a E-SE aspect at around 1100 metres. This slab avalanche is suspected to have released on the buried Christmas surface hoar. On Monday, in the north of the region near Ningunsaw a natural size 3.5 was reported that released on basal facets and ran full path. On Sunday, new wind slabs that formed from reverse loading on south aspects were reported to have released naturally up to size 2.5 in the south of the region. In the north, one size 2.0 natural persistent slab was reported that released down to the ground exposing a bed surface of rock slab.

Uncertain how the band of warm air around treeline has affected the recent wind slabs and persistent weak layer. I suspect that there has been little change in the high alpine and below treeline. Last weeks storm snow has settled a bit, and now there is 40-60 cm in protected areas above the surface hoar that was buried on Christmas. Strong to extreme winds from the north or northeast have developed wind slabs above various old surfaces that include a layer of feathery surface hoar, making wide propagations possible. An earlier weak interface that formed during the early December cold snap can be found in isolated areas buried 100-150 cm deep. The layer consists of preserved surface hoar or weak faceted (sugary) snow. The lower snowpack is well consolidated in deep snowpack areas. In shallow snowpack areas, especially north of Ningunsaw, an old rain crust near the bottom of the snowpack has developed weak facets and might be triggerable from a thin or rocky area on a convex slope.