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, moderate northeast wind, treeline temperatures drop to -30 C.
FRIDAY: Sunny, light to moderate northeast wind, treeline temperatures around -18 C.
SATURDAY: Sunny with a few clouds, light east wind, treeline temperatures around -15 C.
SUNDAY: Mix of sun and cloud, light wind, treeline temperatures around -15 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). These persistent slab avalanches likely failed on a facet and crust layer.
Several small to large (size 1-3) wind slab avalanches were reported earlier this week, some of which were triggered by solar radiation or cornice falls. Over the past week the persistent slab problem has produced fewer avalanches than in the first week of February, but is still showing signs of instability in snowpack tests and warrants careful and cautious assessment.
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. 60-100 cm of snow from February is settling over a layer of surface hoar. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features that are below treeline, however facets above a sun crust may be found on steep south facing features. Snowpack tests results continue to show the potential for propagation on this layer, like this MIN report from Clemina on Monday and this MIN report from the Gorge on Tuesday. The mid/lower snowpack is generally well settled and strong.
Terrain and Travel
- Exercise caution on steep, unsupported slopes.
- Carefully evaluate big/extreme terrain features before committing to them, it may not be full "go" time yet.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Be careful as you transition into wind affected terrain.
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 60-100 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
