Use caution when venturing into big terrain. Persistent weaknesses buried in the snowpack are still capable of producing large destructive avalanches.
Confidence
Good - Forecast snowfall amounts are uncertain
Weather Forecast
5-10 cm of snow overnight and into Saturday morning. This weather system should be out of the Sea to Sky region by Saturday afternoon, giving us clear skies and sunny conditions into next week. Daytime freezing levels are expected to be around 1500 m for the forecast period. Moderate southwesterly alpine winds are expected tonight, then light but gusty south-westerlies for the weekend.
Avalanche Summary
Two reports of large natural avalanches on NE and W aspects from yesterday, and explosive testing by one commercial operator produced a large, 2.5 hard slab avalanche.
Snowpack Summary
Up to 25 cm of low density storm snow is sitting on a thin breakable crust that caps 30-40 cm of recent moist snow on rain crust buried last Saturday. Reports suggest this 5 cm thick solid rain crust exists up to at least 2200m. Strong southwest winds have shifted these new accumulations into touchy wind slabs in exposed terrain. A facet/crust persistent weakness buried mid-March is down approximately 70-130 cm and is still producing hard but sudden results in snowpack tests. This remains the chief concern amongst avalanche professionals in the region due to it's potential for very large avalanches.
Problems
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.
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.