Watch out for slopes being warmed by direct sun. This may locally raise the avalanche danger.
Weather Forecast
Sunday: Clearing up. No snow. Light winds. Freezing level around 900 m.Monday: No snow. Sunny breaks. Light winds. Freezing level around 1200 m.Tuesday: Light snow. Light S winds. Freezing level around 11000 m.
Avalanche Summary
A widespread natural avalanche cycle to size 3.5 occurred on Friday. This included slabs with a suspected failure plane of buried surface hoar/crust layers, and loose wet avalanches which entrained mass as they traveled.Skiers triggered numerous slabs to size 2 earlier in the week, failing on buried surface hoar/crusts which exist at all elevations and on all aspects.
Snowpack Summary
Low density snow had high density snow or rain (snow at alpine elevations around the Duffey; and rain to ridge top around the Coquihalla) piled on top of it at rapid loading rates during the recent storm. Strong southerly winds are likely to have created wind slabs in alpine terrain. Below treeline, rain-soaked snow was very weak during the storm, but should stabilize with cooling temperatures. Surface hoar and/or crust layers in the upper snowpack have been reactive over the last week, creating very touchy conditions. The intense storm and associated avalanche cycle may have gone a long way to ‘clean out’ these weaknesses, but I wouldn’t be too quick to assume anything until we have a lot more information from the field. Direct sunshine may trigger some further shedding of storm snow on Sunday/Monday. The lower snowpack is 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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.