Avalanche Forecast
Issued: Apr 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Cornices, Loose Wet and Wind Slabs.
ldreier,
Avalanche Canada
It's going to be a sunny and warm day with freezing levels rising to 1900 m. Cornices are big and fragile and a hazard on their own if they fail. Be alert to changing conditions on sun exposed slopes during the heat of the day, especially if the snow becomes moist or wet.
Summary
Confidence
Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.
Weather Forecast
A ridge of high pressure over the province brings sunny, dry weather. Freezing levels are forecast to steadily rise through the week.
Monday night: Clear with some clouds and isolated flurries, trace of new snow, moderate to strong east wind, alpine low -15 C, freezing level at valley bottom.
Tuesday: Sunny, moderate to strong east wind, alpine high +1 C, freezing level 1900 m.
Wednesday: Sunny, moderate to strong northeast wind, alpine high +5 C, freezing level 2300 m.
Thursday: Sunny, strong northeast wind, alpine high +6 C, freezing level 2500 m.
Avalanche Summary
Natural and skier controlled wind slabs have been stubborn to trigger and limited to size 1.Â
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.Â
Snowpack Summary
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.
Recent warm weather is expected to have promoted bonding around 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. These persistent weaknesses are definitely worth keeping in mind heading into this next big warmup.
Terrain and Travel
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
- Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
- Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
Problems
Cornices
Cornices will become fragile with rising temperatures, especially when the sun is out. Cornice falls are dangerous in their own right and they can also trigger slabs on slopes below.
Aspects: North, North East, East.
Elevations: Alpine.
Likelihood
Expected Size
Loose Wet
Surface snow can quickly lose cohesion and become unstable with solar warming during the day. Avoid exposing yourself to terrain where a small wet loose release could have big consequences.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Lingering pockets of wind slab may exist in immediate lees of ridge crests and roll-overs at upper elevations. They may remain sensitive to triggering especially where they sit over a crust.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 13th, 2021 4:00PM
