Wind, warming, and incremental snowfall are expected to increase the likelihood of triggering avalanches on Tuesday. Watch for wind-drifted snow and use a conservative terrain strategy to account for a reactive buried weak layer.
Incremental snowfall with strong southwest winds are building a reactive wind slab problem on immediate lee terrain features at upper elevations that may be prone to human triggering. Easier-to-trigger wind slabs have the potential to step down to more deeply buried weak layers, creating larger avalanches.
25-50 cm cm of snow is settling over a layer of surface hoar on sheltered slopes near and above treeline. Although it is suspect on all aspects, this persistent slab problem has been reactive primarily on north-facing slopes between 1800-2300 m.
Monday night: Mostly cloudy, up to 5 cm of snow, areas near Kootenay Pass may see 10+ cm, strong west winds, freezing level 1600 m.
Tuesday: Mostly clear, moderate west winds gusting strong at ridge-top, freezing level rising to 1800 m.
Wednesday: Decreasing cloud, up to 5 cm of snow, west winds decreasing from moderate to light, freezing level dropping from 1300 m to valley bottom by nightfall.
Thursday: Mix of sun and cloud, isolated flurries with trace accumulations, moderate south winds, gusting strong at ridge-top, freezing levels rapidly rising to 2000 m.
On Sunday, several small to large (size 1-2) wind slabs avalanches were reported on lee aspects (northwest, north, northeast) at upper elevations. Check out this MIN report for a helpful example.
Over the weekend, numerous small to large (size 1-2) natural and human-triggered avalanches were reported on the February 22 surface hoar breaking 25-40 cm deep. These avalanches occurred primarily on north-facing aspects between 1800-2250 m. Small wet loose activity was also reported on steep, sunny slopes during the warm temperatures on Friday. In a few cases, these also initiated small slabs on the February 22 surface hoar.
On Thursday, a large (size 2), natural avalanche on an northwest aspect at 2100 m was thought to have stepped-down to the February 13 surface hoar layer.
Incremental snowfall and strong winds from the southwest continue to build reactive wind slabs at upper elevations.
A total 30-50 cm of snow is settling over a layer of feathery surface hoar in open, sheltered areas near and above upper treeline. Warm temperatures last week promoted cohesion in the slab above, priming this layer for human triggering. This problem will be larger where the snow has been drifted by southwest winds into deeper deposits on lee features. Check out the latest forecaster blog that offers a deeper dive into these conditions.
An older layer of surface hoar from February 13th now sits 60-80 cm deep. This weak layer produced significant avalanche activity focused in the east of the region prior to the last storm. While it is likely bonding over time, there is uncertainty around remnant reactivity. Shallower avalanches may have the potential to step-down to this layer. The remainder of the snowpack is well settled.
