Avalanche Forecast
Issued: Feb 11th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
shorton,
Avalanche Canada
Avalanche activity has slowed down, but there is a lingering potential to trigger large avalanches on buried weak layers. Read about managing these conditions in this forecaster blog.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Brrrrrr! Cold and dry conditions persist under arctic air...
THURSDAY NIGHT: Clear skies, light northeast wind, treeline temperatures drop to -25 C.
FRIDAY: Sunny, light to moderate northeast wind, treeline temperatures around -15 C.
SATURDAY: Sunny with a few clouds, light to moderate east wind, treeline temperatures around -15 C.
SUNDAY: Mix of sun and cloud, light wind, treeline temperatures around -12 C.
Avalanche Summary
Avalanche activity has started to slow down over the past few days with reports from Wednesday primarily consisting of small isolated wind slabs and dry loose avalanches (size 1). However, there were two notable human triggered avalanche just outside Glacier National Park on Wednesday where a size 2.5 and a size 3 avalanche were triggered on south and west facing alpine slopes (MIN report). This is a reminder of the lingering possibility of large persistent slab avalanches. There were numerous reports of persistent slab avalanches last weekend and earlier this week including some in lower elevation cutblocks in the southern Selkirks (here and here), a wind slab on a southeast aspect that stepped down to a deeper layer to produce a size 3 avalanche on London Ridge, and a size 1.5 skier triggered slab near Revelstoke (MIN report).
Snowpack Summary
The upper snowpack is becoming soft and faceted with the cold temperatures, while recent wind has left some wind slabs in lee features. 60-120 cm of snow from February is settling over a weak layer of surface hoar that has shown reactivity at treeline or in "treeline-like" features below treeline. On steep south facing terrain this layer may consist of facets on a sun crust. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. This layer will be slow to gain strength and requires careful terrain selection. The mid/lower snowpack is generally strong and settled in most areas.
Terrain and Travel
- Exercise caution on steep, unsupported slopes.
- Carefully evaluate big/extreme terrain features before committing to them, it's not full "go" time yet.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Carefully evaluate steep lines for wind slabs.
Problems
Persistent Slabs
Despite decreasing avalanche danger, there remains a lingering possibility to trigger persistent slab avalanches in isolated steep terrain features. The primary layer of concern is layer of surface hoar, facets, and/or crusts buried 60-120 cm deep throughout the region.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Periods of moderate wind have redistributed recent low density snow into wind slabs on lee features at upper elevations that may be possible to human trigger. Strong sun may weaken cornices, which can act as triggers on slopes below.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 12th, 2021 4:00PM
