With no overnight refreeze the 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
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.
Thursday night: Clear, moderate northeast wind, alpine low +2 C, freezing level 3000 m.
Friday: Sunny, light northeast wind, alpine high +8 C, freezing level 3000 m.
Saturday: Sunny, moderate northwest wind, alpine high +9 C, freezing level 3000 m.
Sunday: Mainly cloudy with isolated flurries, trace of new snow, moderate northeast wind, alpine high +4 C, freezing level lowering to 2000 m.
Avalanche Summary
Numerous wet loose avalanches to size 2 and one size 3 were observed on steep solar aspects on Thursday and Wednesday. Several glide cracks opened up and glide snow avalanches released with the warm temperatures. A few small wet loose avalanches were reported on steep south facing slopes on Monday.
Wind slabs have shown quite limited reactivity last weekend, a few natural and ski cut size 1-1.5 were observed on Saturday.
A couple of natural cornice failures size 2.5 observed on Sunday did not trigger slabs on slopes below.
Neighbouring Glacier National Park reported a few very large (size 3-4) glide slab releases last Thursday. 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 in the alpine. 20-30 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. Reports indicate the snow is bonding well at these interfaces. On North aspects in the alpine, the recent snow sits on dry wintery snow surfaces and possibly surface hoar on wind-sheltered slopes.
Cornices are large, fragile and failing with warm temperatures. Several natural cornice falls were observed recently.
The recent warm weather is 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.
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
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, North West.
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 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.
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
Valid until: Apr 16th, 2021 4:00PM
