Weather Forecast
Synopsis: The true pineapple breaks down Friday and a more zonal flow builds in its place which opens the door to a series of weak systems. Friday: Freezing Level 1400m. Precip: Trace. Wind: Light, SWSaturday: Freezing Level 1200m. Precip: Trace. Wind: Moderate SW gusting to StrongSunday: Freezing Level 1000m in the afternoon, dropping to 500m overnight. Precip: Trace Wind: Light, NW
Avalanche Summary
A widespread natural avalanche cycle to size 2.5 was reported from the Duffey on Wednesday. The Coquihalla reports several wet naturals from size 1 - 2.5 running to the top of the runouts. There was a report of a size 2 skier triggered slab avalanche on a steep southwest aspect in the Steep Creek area (Duffey Lake) on March 8th. Granted, it's a few days old but it highlights the lingering potential for triggering large slab avalanches.
Snowpack Summary
The storm has delivered around 40 cm as of Thursday morning and another 5-10mm/5-15cm is expected Thursday afternoon/evening. This new snow is bonding poorly to the previous snow surface, which includes faceted snow, surface hoar, and/or a crust, but is most concerning where surface hoar is sitting on a crust on previously sun-exposed sheltered treeline slopes. Strong southerly winds in the alpine have created slabs on N - E facing slopes that may be up to a meter in depth. Around a 100 - 150cm below the snow surface is a layer surface hoar buried on February 20th. Although this layer has a history of producing large avalanches, triggering this layer has now become difficult, and would most likely require a very large trigger on a steep, unsupported slope. Below this interface, the 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.