Snow is strengthening over a problematic weak layer, creating conditions prone to human triggering. Travel in avalanche terrain warrants careful evaluation.
20-40 cm cm of snow is settling over a layer of surface hoar on sheltered slopes near and above treeline. Recent warm temperatures have promoted cohesion in the slab above, priming this layer for human triggering. This persistent slab problem is most suspect on north-facing aspects between 1900-2300 m.
Friday night: Partly cloudy, 3-8 cm of snow, strong southwest winds, freezing level dropping to 700 m.
Saturday: Mostly cloudy, isolated flurries with trace accumulations, moderate southwest winds, freezing level 1300 m.
Sunday: Mostly clear, light northwest winds, freezing level 1400 m.
Monday: Mostly clear, moderate west winds, freezing level 1600 m.
Over the past two days, several small (size 1-1.5) natural and human-triggered avalanches have been reported on the February 22 surface hoar layer. These avalanches occurred primarily on north-facing aspects between 1900-2250 m. Small wet loose activity was also reported on steep, sunny slopes on Thursday and 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.
20-40 cm cm of snow is settling over a layer of surface hoar in sheltered areas near and above treeline from February 22nd. Recent warm temperatures have promoted cohesion in the slab above, priming this layer for human triggering. This problem combination will be larger where the snow has been drifted by southwest winds into deeper deposits on lee features.
An older layer of surface hoar from February 13th now sits 50-80 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.
