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
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
The high pressure ridge is forecast to break down early 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.Â
Saturday night: Clear with increasing cloud coverage towards early morning hours and isolated flurries, trace of new snow and rain up to treeline, moderate northerly wind, alpine low +1 C, freezing level around 2800 m and dropping to 1700 m in the early morning hours.
Sunday: Clouds with isolated flurries in the morning and sunny from mid-morning onward, trace of new snow and rain below treeline, moderate to strong northeast wind, alpine high 0 C, freezing level 1700 m.
Monday: Sunny, light northeast wind, alpine high +5 C, freezing level 2100 m.
Tuesday: Mainly sunny, light westerly wind, alpine high +7 C, freezing level 2300 m.
Avalanche Summary
A widespread wet loose avalanche cycle to size 3 and several cornice failures entraining snow on the slopes below were observed on Friday and Thursday (see this MIN). Increased wet loose and potentially wet slab avalanche activity and cornice failures likely continued on Saturday.Â
Several cornices failed recently. Most did not trigger slabs on slopes below except for a few that triggered size 2 slabs on extreme north facing alpine slopes.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 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. Many natural cornice falls were observed recently. Some triggered slabs on the slopes below.
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 triggering buried weak layers increases.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
Wet Slabs
The likelihood of wet slab avalanches will increase during the day with sun exposure. Freezing levels are forecast to stay around 2800 m overnight dropping to 1700 m only in the early morning hours. Clear skies during the night might allow for a shallow refreeze but the snow will likely become moist/wet mid-morning when clouds 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. There is a chance that the heavy load of a failed cornice triggers wet slabs or 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, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Apr 18th, 2021 4:00PM
