Avalanche Forecast
Issued: Dec 23rd, 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
The alpine will stay warm overnight and may make slabs touchy to riders on Thursday.
Summary
Confidence
Weather Forecast
WEDNESDAY NIGHT: Clear skies, 20 to 40 km/h southwest wind, alpine temperature -0 C, above-freezing layer around 2000 m.
THURSDAY: Clear skies, 30 to 50 km/h southwest wind, alpine temperature -1 C, above-freezing layer dissipating near noon.
FRIDAY: Cloudy with snowfall, accumulation 5 cm, 30 km/h south wind, alpine temperature -4 C.
SATURDAY: Cloudy with snowfall, accumulation 5 cm, 20 km/h south wind, alpine temperature -5 C.
Avalanche Summary
Many wind slab avalanches were triggered naturally and by riders on Tuesday. They mostly occurred on southerly aspects due to recent north wind. They most occurred at alpine and treeline elevations. Check out these MINs for a few examples: here, here, and here.
A few large avalanches have been observed on the weak layers described in the snowpack summary within the past week and they were triggered triggered by riders, explosives, and naturally. They occurred on northerly aspects between 1900 and 2100 m and were generally 30 to 50 cm deep.
Snowpack Summary
Warm air is forecast for the alpine, which could mean that recent wind slabs will remain easy to trigger. The wind slabs may be found on all aspects due to variable wind directions.
Two potential concerning weak layers may be 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 but has been reported as spotty across the region.
- 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 the wind blowing and loading the snow in different terrain features over the past two weeks. The layer has been reported as being widespread up to around 2000 to 2200 m.
To date we have mostly seen sporadic avalanche activity on these layers, but they remain possible to trigger where they exist in the mountains.
The remainder of the snowpack is well-settled.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
- 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 be reactive during this warm period, particularly in steep alpine terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A couple problematic layers may be found around 50 to 100 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. There is uncertainty in how warm alpine air will affect the snowpack. It is possible that the warming may increase the potential of humans triggering these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 24th, 2020 4:00PM
