Avalanche Forecast
Issued: Apr 15th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Cornices, Loose Wet and Deep Persistent Slabs.
ldreier,
Avalanche Canada
Solar radiation and warm temperatures will continue to weaken the snowpack and cornices. Avoid exposure to sun exposed slopes and cornices, especially in the afternoon.
Check out the latest Forecaster's Blog on warming and how to stay safe.
Summary
Confidence
High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.
Weather Forecast
A ridge of high pressure continues to bring sunny and dry weather with high freezing levels even at night. On Sunday the ridge is forecast to break down bringing light precipitation and lowering freezing levels.
Thursday night: Clear, moderate to strong northeast wind, alpine low 0 C, freezing level 2400 m.
Friday: Sunny, moderate northeast wind, alpine high +8 C, freezing level 2800 m.
Saturday: Sunny, moderate northwest wind, alpine high +9 C, freezing level 2900 m.
Sunday: Mix of sun and cloud with isolated flurries, up to 5 cm new snow, moderate northwest wind, alpine high +5 C, freezing level lowering to 2000 m.
Avalanche Summary
A large natural cornice fall of size 3 likely released a slab on the northeast facing slope below and was reported on Wednesday. Small wet loose avalanches to size 1 and a couple size 2 were observed on steep solar slopes. A few slab avalanches were reported that might have been triggered by cornices in the last few days.
Natural and skier controlled wind slabs have been stubborn to trigger and limited to size 1 last weekend.Â
Last 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 warm temperatures have made them large and fragile.Â
Snowpack Summary
The snow surface consists of a melt-freeze crust on solar aspects and shaded aspects up to treeline which transitions into moist/wet snow during the day. Dry snow can still be found on northerly aspects in the alpine. 10-30 cm of recent snow has 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 the snow is bonding well at these interfaces.
Cornices are large, fragile and primed to fail with warm temperatures. Many natural cornice falls were recently observed. Some triggered slabs on the slopes below.
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.Â
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.
- Avoid sun exposed slopes, especially if snow surface is moist or wet.
- The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
Problems
Cornices
Cornices are large and fragile. Warm temperatures and sun exposure will lead to cornice falls. Cornice falls are dangerous on their own and they can trigger slabs on slopes below. There is a chance that the heavy load of a failed cornice triggers deep persistent slabs.
Cornices often break further back than expected. Give them a wide berth when travelling on ridgetops. Avoid slopes with cornices overhead, especially if they are exposed to the sun and during the heat of the day. Take into account long runout distances when travelling underneath slopes with cornices overhead.
Aspects: North, North East, East, South East, South.
Elevations: Alpine.
Likelihood
Expected Size
Loose Wet
Surface snow can quickly lose cohesion and become unstable with strong solar radiation and warm temperatures. Freezing levels are forecast to stay around 2400 m overnight. Clear skies during the night might allow for a shallow refreeze but the snow will likely become moist/wet in the early morning hours.
Back off slopes when the snow becomes moist or wet. Avalanches might grow larger than expected by entraining snow along the way and reach lower elevations. Avoid exposing yourself to slopes that are exposed to the sun, especially in the afternoon. Be aware what is above you when leaving your skiing or riding area.
Aspects: South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Each day of warm weather increases the likelihood of reactivating buried weak layers. It is uncertain if and when large slab avalanches may release but the possibility remains during this warm period. Deeper releases are most likely in shallow snowpack areas on the eastern slopes of the Purcells. Heavy cornice falls might trigger large slab avalanches. Skiers and riders might be able to trigger buried weak layers in rocky and shallow snowpack areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 16th, 2021 4:00PM
