With multiple warm days in a row and high overnight freezing levels it is important to start and finish your day early. Look for north facing objectives without overhead cornices. Plan your egress route carefully.
Check out the 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 freezing levels around 3000 m even at night. On Sunday the ridge is forecast to break down bringing light precipitation and lowering freezing levels.
Friday night: Clear, light north wind, alpine low +3 C, freezing level 3000 m.Â
Saturday: Sunny, light northwest wind, alpine high +9 C, freezing level 3000 m.
Sunday: Mainly cloudy with isolated flurries, 5-10 cm new snow and rain at treeline and below, moderate to strong northeast wind, alpine high +6 C, freezing level lowering to 1800 m during the day.
Monday: Mainly sunny, light north wind, alpine high +5 C, freezing level 2000 m.
Avalanche Summary
Numerous wet loose avalanches to size 2 and several wet slab avalanches of size 2.5-3 and one size 3.5 were observed on steep solar aspects on Thursday. A few small wet loose avalanches in steep rocky terrain were reported on Tuesday as well as a small slab avalanche triggered by a skier on a northeast facing alpine slope.Â
A couple of recent natural cornice failures size 2.5 did not trigger slabs on slopes below except for one which triggered small slab avalanches.
Neighbouring Glacier National Park reported a few very large (size 3-4) glide slab releases last week. Glide slabs are hard to predict and can release at any time, so it is important to avoid slopes with glide cracks.
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 might still be found on northerly aspects high in the alpine. 20-40 cm of recent snow has formed isolated pockets of wind slab on leeward slopes and behind terrain features. The recent snow sits on a series of melt-freeze crusts on all aspects below 1900 m and southerly aspects to mountain top. On North aspects in the alpine, the recent snow sits on dry wintery snow surfaces and possibly surface hoar on wind-sheltered slopes.Â
Cornices are large, fragile and failing with warm temperatures. Several natural cornice falls were observed recently.Â
Previous periods of warm weather are expected to have helped old persistent weak layers heal, including a few crusts buried over the last month as well as a facet layer 150 cm deep from the mid-February cold snap. However, with each day of warm weather the likelihood of persistent slab avalanches increases slightly.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.
- Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
Problems
Wet Slabs
The likelihood of wet slab avalanches will increase with yet another hot and sunny day. Freezing levels are forecast to stay at 3000 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. The upper snowpack can quickly lose cohesion and become unstable with strong solar radiation and warm temperatures.
Wet loose avalanche activity can be expected, especially during the heat of the day.
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
Cornices
Cornices are large and fragile. Warm temperatures and sun exposure will lead to cornice falls. Many natural cornice failures were reported recently. Cornice falls are dangerous on their own and they can trigger slabs on slopes below.
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.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Apr 17th, 2021 4:00PM
