Strong solar radiation and warm temperatures will weaken cornices and the snowpack. Avoid overhead hazard, especially in the afternoon. The danger rating is for the hottest time of the day. Check out this blog on warming and how to stay safe.
Cornices are large and will become more fragile with rising temperatures and sun exposure. Cornice falls are dangerous in their own right and they can trigger slabs on slopes below.
Surface snow can quickly lose cohesion and become unstable with strong solar radiation and warm temperatures. Avoid exposing yourself to sunny slopes, especially in the afternoon.
A ridge of high pressure over the province continues to bring sunny, dry weather. Freezing levels are forecast to steadily rise through the week.
Tuesday night: Clear, strong northeast wind, alpine low -13 C, freezing level at valley bottom.
Wednesday: Sunny, moderate to strong east wind, alpine high +4 C, freezing level 2300 m.
Thursday: Sunny, moderate northeast wind, alpine high +8 C, freezing level 2500 m.
Friday: Sunny, moderate northeast wind, alpine high +9 C, freezing level 2800 m.
Natural and skier controlled wind slabs have been stubborn to trigger and limited to size 1.
On Thursday, a significant natural cornice failure triggered a persistent slab on the slope below and resulted in a size 3 avalanche. This occurred on a high alpine steep east-facing slope. This is an important reminder to stay well back from ridgetops that may be corniced and avoid slopes with overhead cornice exposure especially under the current conditions where recent rapid growth and daytime warming has made them large and fragile.
The snow surface consists of a crust on solar aspects. Dry snow can be found on northerly slopes at treeline and in the alpine. 10-30 cm of recent snow may have formed isolated pockets of wind slab on leeward slopes and behind terrain features. The new snow sits on a series of melt-freeze crusts on all aspects below 1900 m and southerly aspects to mountain top. Reports indicate snow is bonding well at these interfaces.
Widespread crust layers formed over the last month in the mid to upper snowpack. One widespread crust from mid-March found 30-60 cm deep saw isolated instances of large solar-triggered slab avalanches during the last sunny period. The early November crust is buried down 180-200 cm with faceted crystals above and below it.
With each day of warm weather the likelihood of deep persistent slab avalanches will increase.
