Areas with the best snow (higher elevation, north-facing slopes) align with where large avalanches are possible. Travel in avalanche terrain warrants careful evaluation of wind-drifted snow and more deeply buried weak layers on Sunday.
5-10 cm of new snow with moderate ridge-top winds from the southwest are building a reactive wind slab problem on immediate lee terrain features at upper elevations that may be prone to human triggering.
25-50 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.
Saturday night: Decreasing cloud, isolated flurries with trace accumulations, moderate northwest winds, freezing level dropping below valley bottom.
Sunday: Mostly clear, increasing cloud in the afternoon, light northwest winds, freezing level 1400 m.
Monday: Mostly clear, moderate west winds, freezing level 1600 m.
Tuesday: Mix of sun and cloud, isolated flurries with trace accumulations, moderate southwest winds gusting strong at ridge-top, freezing level rising to 1800 m.
Since Thursday, numerous 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 during the warm temperatures 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.
5-10 cm of snow fell on Saturday with moderate ridge-top winds from the southwest drifting it onto immediate lee features.
A total 30-50 cm of snow is settling over a layer of feathery 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 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 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.
