Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
Wind slabs may linger and weak layers exist in the snowpack at a prime depth for riders to trigger.
Summary
Confidence
Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.
Weather Forecast
SUNDAY NIGHT: Partly cloudy, 20 to 40 km/h west wind, alpine temperature -6 C, freezing level 1000 m.
MONDAY: Snow, accumulation 5 cm, 20 km/h north wind, alpine temperature -9 C.
TUESDAY: Clear skies, 10 km/h north wind, alpine temperature -11 C.
WEDNESDAY: Mix of sun and cloud, 10 km/h southwest wind, alpine temperature -2 C, freezing level 1700 m.
Avalanche Summary
A few large avalanches were triggered on the buried weak layers described in the snowpack summary on Saturday. They were triggered using explosives as well as by riders. They occurred on northerly aspect in alpine terrain (2100 m) and were generally 30 to 50 cm deep.
Otherwise, small to large (size 1 to 2) storm and wind slab avalanches were triggered by riders and explosives on Friday to Sunday. They generally occurred at treeline and alpine elevations on northerly terrain features and within the top 50 cm of the snowpack.
Snowpack Summary
Wind slabs are likely to be found at treeline and alpine elevations on northerly to easterly leeward slopes. In sheltered terrain, numerous storm snow interfaces may be found in the top 50 cm of the snowpack, which may take a couple of days to bond.
Two concerning weak layers are present in the snowpack. The shallower layer, being around 50 to 80 cm deep, includes feathery surface hoar crystals. There is uncertainty in the distribution of this layer, but the most likely place to find it would be in terrain features sheltered from the wind around treeline and lower alpine elevations. The more widespread weak layer includes sugary faceted grains that overlies a hard melt-freeze crust. This layer is generally found around 50 to 100 cm deep and is widespread up to around 2000 to 2200 m.
The remainder of the snowpack is well-settled.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Wind Slabs
Strong southeast to southwest wind on the weekend formed wind slabs at and above treeline. Expect to find them on lee terrain features adjacent to ridges.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A couple problematic layers exist around 50 to 100 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. Large avalanches have been triggered on these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
