Strong southerly wind, continued precipitation and lowering freezing levels are expected to drive fresh storm slab development through Friday. Wind slabs are likely to be found in unusual locations, welcome back to winter!
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
A rather complex weather pattern continues to deliver precipitation to the Sea to Sky region. Lower freezing levels Thursday night and Friday should allow for snow at lower elevations. Precipitation is expected to diminish Friday night with potential for some clearing Saturday.THURSDAY NIGHT: Freezing level lowering from 1200 m to 400 m, moderate to strong south/southwest wind, 1 to 10 mm of precipitation. FRIDAY: Broken cloud cover, freezing level starting near valley bottom rising to 1000 m, moderate to strong south/southwest wind, 5 to 12 mm of precipitation expected.SATURDAY: A few clouds, freezing level beginning at 500 m rising to 1100 m, light south/southwest wind, no significant precipitation expected. SUNDAY: Scattered cloud cover, freezing level holding around 800 m, light west/southwest wind, a few mm of precipitation possible.
Avalanche Summary
Thursday's storm likely generated natural avalanche activity that was probably most prevalent at upper elevationsThere was a rather anomalous size 3.5 that was seen on the Cheakamus Glacier from Whistler March 15th. We don't have details on the failure plane of this avalanche, but it may have run on the mid-February crust.
Snowpack Summary
Thursday and Friday's storm snow is sitting on a mix of moist grains, crusts, surface facets and surface hoar. The crust is widespread on solar aspects at all elevations. Both treeline and alpine elevations facing north and east have significant surface hoar and near surface facet development. Some west facing features may have surface hoar on top of a crust which would be particularity problematic. The storms transition from warm to cold should be good for our snowpack in the long term, but the storm is expected to continue to generate touchy storm slabs. 5 to 20 cm of wind distributed snow fell last week which came to rest on the mid-March crust on all but high elevation north aspects.50 to 100 cm below the surface is a combination of facets, surface hoar, and/or crust known as the mid-February layer. This interface has not been active recently, but it does continue to produce resistant planar results in snowpack tests. The mid and lower snowpack is strong and well settled.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.