Avalanche Forecast
Issued: Dec 27th, 2020 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
Soft slabs in wind loaded features may remain sensitive to human triggers at upper elevations. Keep an eye on steep south facing slopes for solar triggered point releases in recent snow.
Summary
Confidence
Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.
Weather Forecast
Sunday night: Mostly cloudy, light southwest wind, freezing level 800 m.
Monday: Sun and cloud, light northwest wind, alpine temperature -4 C, freezing level 1000 m.
Tuesday: Increasing cloud, light to moderate southwest wind, alpine temperature -5 C, freezing level 600 m.
Wednesday: Cloudy, moderate southwest wind, alpine temperature -7 C, freezing level 800 m.
Avalanche Summary
Storm slabs and cornices were reported to be touchy during the storm on Saturday, skier end explosive control work producing storm slab avalanches size 1-2.
Last week, numerous wind slab avalanches were reported, triggered naturally and by riders at treeline and alpine elevations. Check out these MINs for a few examples: here, here and here.
A few large avalanches were observed last week, running on buried weak layers (described in snowpack summary). Most occurred on north to east aspects in the alpine. A size 2.5 reported Thursday from a coastal glaciated area west of the Squamish river was on a southeast aspect, 100 m wide with crown depth 40-80 cm deep.
Snowpack Summary
15-30 cm of recent snow has been redistributed by strong south to east winds, depositing deep pockets of storm slab into lee terrain features.
Two potential concerning weak layers may be present in the snowpack:Â
- The shallower layer, around 60 to 100 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.Â
- 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 120 cm due to the wind scouring 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.Â
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 with wind loaded pockets, especially near ridge crests and roll-overs.
- Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
- Conditions may have improved, but be mindful that deep instabilities are still present.
Problems
Storm Slabs
On Monday, storm slabs will likely remain most reactive in wind loaded lees such as below ridge crests and roll overs. New snow may become increasingly sensitive to triggering when touched by the sun for the first time. Watch for loose dry point releases in steep south facing terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A couple problematic layers may be found around 50 to 120 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. There remains potential for storm slab avalanches to step down to these layers, resulting in large and destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 28th, 2020 4:00PM
