Avalanche Forecast
Issued: Dec 22nd, 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
An alpine warm-up may stress the snowpack and increase the likelihood of human triggering.
Summary
Confidence
Moderate - Uncertainty is due to difficult to forecast freezing levels.
Weather Forecast
TUESDAY NIGHT: Clear skies, 20 to 30 km/h northwest wind, alpine temperature -6 C.
WEDNESDAY: Mix of sun and cloud, 20 to 40 km/h west wind, alpine temperature -2 C, freezing level rising to 1600 m.
THURSDAY: Clear skies, 20 to 30 km/h south wind, alpine temperature 0 C, freezing level 2200 m.
FRIDAY: Cloudy with snowfall, accumulation 5 cm, 10 to 30 km/h south wind, alpine temperature -4 C.
Avalanche Summary
Numerous wind slab avalanches were triggered naturally and by riders on Tuesday. The occurred on southerly aspects due to recent north wind. They most occurred at alpine and treeline elevations.
The latest observed avalanche on the weak layers described in the snowpack summary occurred on December 19, where a few large avalanches were triggered by riders and explosives. They occurred on northerly aspect in alpine terrain (2100 m) and were generally 30 to 50 cm deep.
Snowpack Summary
Wind slabs may linger at treeline and alpine elevations on all aspects due to wind starting from the south and shifting to the north. These strong winds mean that variable conditions and snow depths will be found in alpine terrain. In sheltered terrain, numerous storm snow interfaces may be found in the top 50 cm of the snowpack, which may take a bit of time 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. This layer may be found in sheltered terrain features at treeline and lower alpine elevations. The more widespread weak layer includes sugary faceted grains that overlies a hard melt-freeze crust. This layer ranges in depth from 10 cm to 100 cm due to wind effect. The layer has been reported as being widespread up to around 2000 to 2200 m.Â
The remainder of the snowpack is well-settled.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Extra caution for areas experiencing rapidly warming temperatures for the first time.
- 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
Wind slabs may be found on all aspects in exposed terrain due to shifting winds. These slabs have been reactive to riders and may continue to linger.
Aspects: All aspects.
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. A warming trend is forecast and there is uncertainty in how it will affect the snowpack. It is possible that the warming may make it more possible for humans to trigger these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 23rd, 2020 4:00PM
