Avalanche Forecast
Issued: Feb 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Watch for uncharacteristic wind slabs at upper elevations as east winds continue. Uncertainty about triggering large avalanches warrants careful terrain selection. Read about managing these conditions in this forecaster blog.
Summary
Confidence
Weather Forecast
FRIDAY NIGHT: Clear, light to moderate east wind, alpine temperatures around -20 C.
SATURDAY: Sunny with a few clouds, light to moderate east wind, alpine temperatures around -18 C.
SUNDAY: Mix of sun and cloud, light south wind, alpine temperatures around -15 C.
MONDAY: Sunny with a few clouds, light variable wind, alpine temperatures around -12 C.
Avalanche Summary
Small to large (size 1-3) natural and human-triggered wind slab avalanches have been reported consistently throughout the week in the alpine, some of which were triggered by solar radiation or cornice falls. This MIN report from neighboring Glacier National Park on Thursday offers a helpful visual of this avalanche activity. Operators have also reported numerous recent dry loose avalanches (size 1-1.5).
On Wednesday, there were two notable large (size 2.5-3) human-triggered avalanches reported just outside of Glacier National Park on south and west facing alpine slopes (MIN report). These persistent slab avalanches likely failed on a facet and crust layer buried Jan 24th.
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 assessment.
Snowpack Summary
On Thursday, winds picked up out of the east/northeast with enough gusto to move snow around, giving new life to wind slab problems in the region. Watch for wind slabs in uncharacteristic places at upper elevations as easterly winds continue.
While wind may be forming slabs in lee features, the upper snowpack is becoming soft and faceted with the cold temperatures. 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
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Approach lee and cross-loaded slopes with caution.
- Cornice failure may trigger large avalanches.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Wind Slabs
An uptick and shift to easterly winds on Thursday formed new wind slabs at upper elevations that will likely remain sensitive to human triggers. Given the recent variability in wind direction and unusual loading pattern, treat all aspects as suspect. Cornices may be reaching their breaking point.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Valid until: Feb 13th, 2021 4:00PM
