As wind picks up in the alpine Thursday afternoon you need to watch for the formation of fresh wind slabs which will add to the existing wind slab problems. The best riding will be found in wind sheltered areas.
Southwest wind is expected to pick up in the alpine Thursday afternoon, stay alert for the formation of fresh slabs. This adds to the work that shifting winds from all compass directions have produced in the last week. Given the potential for cross-loading and reverse-loading, treat all aspects as suspect. Cornices may be reaching their breaking point and can act as triggers.
It remains possible 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.
Southwesterly flow starts setting up to deliver dribs and drabs of snow and a rising freezing level.
WEDNESDAY NIGHT: Freezing level at valley bottom, light west/northwest wind, no snow expected.
THURSDAY: A few clouds at dawn building to broken cloud cover in the afternoon, light southeast wind at most elevations, strong southwest wind at ridgetop, trace of snow possible during the day with 2 to 6 cm expected Thursday night.
FRIDAY: Overcast, freezing level rising to about 900 m, moderate to strong west/southwest wind, 2 to 10 cm of snow possible during the day with an additional 1 to 5 cm Friday night.
SATURDAY: Overcast, freezing level beginning at valley bottom rising to about 1000 m, moderate to strong southwest wind, trace of snow possible during the day with another 5 to 8 cm Saturday Night.
Avalanche activity over the last few days has been limited to small dry loose avalanches (size 1-1.5). In the adjacent Glacier National Park Region there were some large natural wind slab avalanches reported from extreme north facing terrain features on Monday.
The second week of February produced fewer persistent slab avalanches than the first week of February. But, the late January persistent weak layer is still showing signs of instability and warrants assessment. Last Friday, operators reported a large (size 2.5) natural avalanche on a southeast aspect in the alpine, releasing on facets. This MIN report from the Gorge is a helpful example of the lower elevation slopes where the surface hoar has been preserved.
A few centimetres of snow have begun to accumulate over a variety of surfaces including sugary facets, feathery surface hoar, and wind-affected snow that formed as a result of last week's dry, cold weather.
As southwest winds begin to pick up Thursday afternoon fresh wind slabs are likely to form.
Winds have varied in strength and direction over the past week, loading cornices and forming wind slabs at upper elevations that may still be possible to trigger. Watch for these wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. Wind slabs may overlie weak, sugary, faceted snow, meaning that they could break wider than expected and will likely be slow to bond.
60-100 cm of snow from February is settling over a layer of surface hoar buried in late January. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features, like cutblocks, that are below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust, which has produced notable low probability/high consequence avalanches and requires a conservative approach. Read about managing these conditions in this forecaster blog.
The mid/lower snowpack is generally well settled and strong.
