Caution should be used when venturing into big terrain. Buried weak layers are still capable of producing large destructive avalanches.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
Around 5 cm of snow is expected this afternoon through to Saturday morning. Then things start to dry out with a mix of sun and cloud on Sunday. Daytime warming will push the freezing level to around 1600 m for the forecast period. Moderate southwesterly alpine winds are expected on Friday then light but gusty south-westerlies for Saturday before shifting to south-easterlies on Sunday
Avalanche Summary
Reported Thursday were several size 2 to 2.5 natural avalanches in steep high alpine terrain, attributed to wind loading. Cornice failures have also been reported recently, triggering large avalanches. We are also hearing of sluffs in steep solar affected alpine terrain.
Snowpack Summary
20-30 cm of low density storm snow is sitting on a strong and supportive rain crust that was buried last Saturday and extends as high as 2100m. West through southwesterly winds have shifted these new accumulations into touchy wind slabs in exposed lee terrain. A facet/crust persistent weakness that was buried in mid-March is now approximately 50-100 cm down. In recent snowpack tests, it was found down 55 cm near the Duffey Lake Road and produced moderate sudden results. This remains the chief concern amongst avalanche professionals in the region because of 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.