Avalanche Forecast
Regions: Purcells.
Lingering wind slabs may remain reactive to human triggers on lee features below ridgetops in the alpine. Expect natural wet loose avalanches to occur on solar aspects if the sun comes out.
Confidence
High -
Weather Forecast
A ridge of high pressure sets up over the province bringing sunny, dry weather. Freezing levels are forecast to steadily rise through the week.
Sunday night: Partly cloudy. Light wind switching east. Alpine temperature around -9. Freezing level valley bottom.
Monday: Mix of sun and cloud. Light east wind. Alpine temperature around -6. Freezing level 1600 m.
Tuesday: Mix of sun and cloud. Moderate northeast wind. Alpine temperature around -3. Freezing level 1800 m.
Wednesday: Mix of sun and cloud. Moderate to strong northeast wind. Alpine temperature around -1. Freezing level 2300 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 from the slope below size 3. 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 the next big warmup.
Terrain and Travel
- Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
- 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
Avalanche Problems
Cornices
Cornices are often fragile this time of year, 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: Possible
Expected Size: 2 - 3
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: Unlikely - Possible
Expected Size: 1 - 1.5
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: Likely
Expected Size: 1 - 1.5