Avalanche Forecast
Issued: Feb 27th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs.
mconlan,
Avalanche Canada
Be wary of incremental loading over a layer of surface hoar. Once a threshold amount of snow accumulates and forms slab properties, slab avalanches will be easy to trigger at all elevations and on all aspects. Conservative decision-making is warranted.
Summary
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
THURSDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm, moderate southwest wind, alpine temperature -6 C, freezing level 1400 m.
FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, light to moderate southwest wind, alpine temperature -5 C, freezing level 1500 m.
SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, light to moderate southwest wind, alpine temperature -9 C, freezing level 1000 m.
SUNDAY: Morning snowfall then a mix of sun and cloud, accumulation 5 cm, light west wind, alpine temperature -10 C.
Avalanche Summary
Many small (size 1 to 1.5) and a few large (size 2) storm/persistent slab avalanches were triggered by humans on Tuesday and Wednesday. They occurred at all elevation bands, between 1600 m and 2300 m, and generally on northwest to east aspects but a couple released on south aspects. They were commonly 20 to 40 cm deep and released on the surface hoar layer described in the Snowpack Summary.
Snowpack Summary
Around 30 to 40 cm of snow overlies a widespread layer of surface hoar that was reported to be between 10 and 20 mm in size and at all elevations. This same layer of surface hoar has been reported as sitting on a thin melt-freeze crust on sun-exposed aspects, which is a particularly nasty combination. This snow has been reactive to human traffic and natural triggers, particularly around treeline and alpine elevations where the overlying snow has slab properties. As this snow continues to gain slab properties with more snow, wind, and a warming trend, activity on this layer is expected to increase and avalanches will grow in size.
The early-February melt-freeze crust down 50-100 cm is dormant but should be monitored. The remainder of the mid and lower snowpack is generally well-settled and strong.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Stick to simple terrain or small features with limited consequence.
- Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Problems
Persistent Slabs
A widespread layer of surface hoar found at all elevations and on all aspects has been reactive to human traffic. The layer is buried around 30 to 40 cm deep. On south aspects, the surface hoar may be found overlying a melt-freeze crust, which is a particularly nasty combination. To date, the layer has been most reactive between around 1700 and 2300 m and where the overlying snow has gained slab properties from snow load and wind affect. This elevation band of reactivity may increase in the coming days as new snow, strong wind, and a warming trend may increase slab properties.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 28th, 2020 5:00PM
