A forecast change in wind direction means that wind slabs may be found on all aspects.
The potential exists to trigger deeper weak layers, choose conservative terrain.
Moderate to strong winds will likely continue to form fresh and reactive wind slabs. A forecast change in wind direction on Friday will mean that wind loading may be found on all aspects.
Cornices have experienced rapid growth with recent strong west to southwest winds. Use caution on ridgelines, and in terrain with cornices above.
There may be a lingering possibility of triggering persistent slab avalanches in isolated steep terrain features. The primary layer of concern is layer of surface hoar, facets, and/or crusts buried 40-80 cm deep throughout the region.
THURSDAY NIGHT - Mainly cloudy with flurries, 5 cm / moderate to strong west wind / alpine low temperature near -10
FRIDAY - Mainly cloudy with a few flurries / moderate northwest wind / alpine high temperature near -9
SATURDAY - A mix of sun and cloud / light to moderate northwest wind / alpine high temperature near -11
SUNDAY - A mix of sun and cloud / moderate to strong west wind / alpine high temperature near -7 / freezing level 1500 m
On Wednesday, there were a few reports of natural and explosive triggered size 2 storm and wind slab avalanches, as well as a few natural and explosive triggered cornices up to size 3. There were also a few notable remotely triggered avalanches reported in the north of the region that are suspected to have failed on the recently buried facets. The MIN report can be viewed here.
Reports of storm slab avalanches from Monday and Tuesday near Golden include size 2-2.5 naturals, some of which were cornice triggered; size 2 explosive results; and human-triggered size 1's.
Near Invermere, natural, explosive and human-triggered wind slab avalanches were mainly in the 1-1.5 size range on Monday and Tuesday. A natural size 2 wind slab on a northeast aspect is suspected to have stepped down to deeper persistent layers.
Earlier in February, there were a few reports of large avalanches (size 2.5-3) on southeast aspects in the alpine, likely releasing on a layer of facets on a crust (see a photo here), and a large human-triggered avalanche (size 2.5) on surface hoar near Quartz Creek.
Recent snowfall amounts have varied throughout the region from less than 10 cm in the east to 40-50 cm along the western part of the region, and near Golden. At upper elevations, this snow has been blown into slabs in lee terrain features.
The recent snow sits on weak, faceted snow that formed during the last cold snap. We expect this interface to stick around for a while, and it may be tricky to manage due to the highly variable depth of the layer throughout the region. This MIN from one of the highest snowfall areas gives a great account of this variability, even on a small scale.
A weak layer that formed in late January is now 30-90 cm deep. In the northern Purcells, this layer has been reported as a surface hoar layer at treeline and below, but a combination of facets or crusts could exist at all elevations. A couple of recent wind slab avalanches near Golden and Invermere have been suspected to have stepped down to this layer in the alpine.
The northern Purcells also have an older surface hoar layer that can still be found 60-120 cm deep at treeline. Additional weak layers may exist near the bottom of the snowpack and steep rocky areas with a shallow or thin to thick snowpack should be considered suspect trigger points.
