Avalanche Forecast
Issued: Dec 19th, 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
Snow and strong wind tonight will form new slabs and continue to load buried weak layers.
Summary
Confidence
Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.
Weather Forecast
SATURDAY NIGHT: Snow, accumulation 10 to 20 cm with local amounts up to 30 cm possible, 60 to 80 km/h southwest wind, alpine temperature -2 C, freezing level 1700 m.
SUNDAY: Cloudy, 40 to 60 km/h west wind, alpine temperature -7 C, freezing level 1000 m.
MONDAY: Snow, accumulation 20 to 30 cm, 30 to 50 km/h south wind, alpine temperature -5 C.
TUESDAY: Clear skies, 10 to 20 km/h north wind, alpine temperature -9 C.
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 and Saturday. They generally occurred at treeline and alpine elevations on northerly terrain features and within the top 50 cm of the snowpack.
Snowpack Summary
Saturday night's snowfall will accumulate with strong southwest wind, forming wind slabs in exposed terrain. These will overly previous storm layers within the top 50 cm of the snowpack. The freezing level is expected to reach around 1700 m, so rain followed by a cooling trend will limit avalanche concerns below that elevation.
This snow will continue to load a couple weak layers 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 2200 m.
The remainder of the snowpack is well-settled.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
- 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
Around 20 cm of snow with strong southwest wind will form new wind slabs in exposed terrain. Use particular caution immediately adjacent to ridges, where the slabs will likely be thickest and touchiest. The storm snow may still be touchy in sheltered terrain features, so check for the bond of the snow prior to committing to avalanche terrain.
Aspects: North, North East, East, South East, South, 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. The likelihood of triggering them will increase with further snow load on Saturday night.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 20th, 2020 4:00PM
