Avalanche Forecast
Issued: Jan 4th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
Avalanche hazard will increase as snowfall resumes and fresh storm slabs build in the afternoon. Be on alert for signs of instability in recent snow.
Summary
Confidence
Weather Forecast
Monday night: Flurries, 5-10 cm, moderate southwest wind, freezing level 700 m.
Tuesday: Snow starting in the afternoon, 5-15 cm, strong southerly wind, alpine high -5, freezing level 1100 m.
Wednesday: Snow overnight then flurries, 15-25 cm, southwest wind easing to light, alpine high -6, freezing level 1100m.
Thursday: Sun and cloud, light southwest wind, alpine high -6, freezing level 900m.
Avalanche Summary
A large, natural storm slab avalanche cycle size 3-4 occurred near Pemberton over the weekend. Natural and explosive triggered storm slabs size 1-2 were reported elsewhere. This MIN report from Friday illustrates the active avalanche conditions during this storm.
Persistent slab avalanche activity has tapered significantly since the cycle early last week, but persistent slabs size 2-2.5 were still triggerable by explosives on weekend. Events from last week include:
- A fatal avalanche in the South Coast Inland region (near the Sea to Sky boundary) north of Pemberton in the Railroad Pass area last Monday. It was reported to be a size 2 persistent slab avalanche on a west aspect, around 1650 m. The RCMP press release can be viewed here, and the Avalanche Canada report can be found here.
- A size 2.5 avalanche was triggered on Monday by a skier on Rainbow Mountain, which resulted in a full burial and, thankfully, a successful rescue. The avalanche failed on a 60 cm deep crust and facet layer on a northeast aspect around 1800 m.
These avalanches highlight the ongoing potential to trigger persistent weak layers in the snowpack.
Snowpack Summary
Over 100 cm of recent storm snow has seen extensive wind effect at upper elevations, with scoured windward aspects, wind slabs in lee features and growing cornices at ridgetop.
The snowpack is currently quite complex. The layer of greatest concern is a melt-freeze crust from early December, found around 100-200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. There have been several recent large natural and human triggered avalanches on this layer and new snow loads as well as large loads from storm slab avalanches have potential to trigger these layers.
The remainder of the snowpack is well-settled.
Terrain and Travel
- Watch for avalanche hazard to increase throughout the day.
- Choose conservative terrain and watch for clues of instability.
- Be careful as you transition into wind affected terrain.
- Be mindful that deep instabilities are still present and have produced recent large avalanches.
Problems
Storm Slabs
Storm slabs will likely become increasingly reactive in the afternoon as snowfall resumes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple of problematic layers may be found around 100 to 200 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. These layers have shown a downtrend in activity since early last week but there remains potential for avalanches to step down to these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 5th, 2021 4:00PM
