Yet another day without a good overnight refreeze. Temperatures will drop in the morning, but sun exposure can deteriorate conditions rapidly. The rating is for the hottest time of the day.
Check out the Forecaster's Blog on warming and how to stay safe.
Summary
Confidence
Weather Forecast
The high pressure ridge is forecast to break down Sunday morning bringing light precipitation and lowering freezing levels followed by a classic diurnal melt-freeze cycle on Monday for the next couple of days.
Saturday night: Clear with increasing cloud coverage towards the morning, light to moderate northwest wind, alpine low +1 C, freezing level at 3000 m and lowering to 2500 m in early morning hours.
Sunday: A few clouds with isolated flurries in the morning and mainly sunny from mid-morning onward, trace of new snow and rain below treeline, moderate to strong northeast wind, alpine high +2 C, freezing level dropping to 1700 m in the morning.
Monday: Mainly sunny, light to moderate northerly wind, alpine high +4 C, freezing level 2000 m.
Tuesday: Mainly sunny, light variable wind, alpine high +7 C, freezing level 2300 m.
Avalanche Summary
On Friday numerous wet loose avalanches on all aspects and wet slabs to size 3 on solar aspects were reported. Numerous wet loose avalanches to size 2 were observed on steep solar aspects on Thursday and Wednesday (see this MIN). Several wet slab avalanches of size 2.5-3 and one size 3.5 were reported on Thursday.
A few recent natural cornice failures of size 2.5 did not trigger slabs on slopes below.
Several glide cracks opened up and glide snow avalanches released with the warm temperatures. 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 2200 m which transitions into moist/wet snow during the day. Dry snow might still be found on northerly aspects in the alpine above 2400 m. 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. 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.
Recent 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.
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 during the day with sun exposure. Freezing levels are forecast to stay at 3000 m overnight dropping to 1700 m in the morning. Mostly clear skies during the night might allow for a shallow refreeze but the snow will likely become moist/wet mid-morning when clouds slowly dissipate and the sun comes out. The upper snowpack can quickly lose cohesion and become unstable with strong solar radiation.
Wet loose avalanche activity can be expected on sunny slopes and below treeline, 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, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Apr 18th, 2021 4:00PM
