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
Weather Forecast
A ridge of high pressure continues to bring sunny and dry weather with freezing levels around 3000 m even at night. On Saturday night the ridge is forecast to break down bringing light precipitation and lowering freezing levels.
Friday night: Clear, light northwest wind, alpine low +2 C, freezing level 2900 m.
Saturday: Sunny, light northwest wind, alpine high +6 C, freezing level 3000 m.
Sunday: Mix of sun and cloud with isolated flurries, trace of new snow and rain below treeline, moderate to strong northeast wind, alpine high +2 C, freezing level lowering to 1700 m.
Monday: Sunny, light northeast wind, alpine high +4 C, freezing level 2100 m.
Avalanche Summary
A widespread wet loose avalanche cycle to size 3 and several cornice failures entraining snow on the slopes below were reported on Friday and suspected to have happened over the last few days (see this MIN).
Several small wet loose avalanches to size 1.5 on solar aspects in the alpine were reported on Tuesday.
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.
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.
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.
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 with yet another hot and sunny day. Freezing levels are forecast to stay around 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. 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 17th, 2021 4:00PM
