A reactive layer of surface hoar lurks in the snowpack and requires conservative terrain selection - stick to low angle slopes, be suspect of open glades and any slope with terrain traps, and bring an extra puffy - it's cold.
Variable wind has formed reactive slabs on multiple aspects, and wind will continue to impact loose snow. Avalanches will be most likely in wind loaded areas and where the snow feels stiff or punchy.
40-65 cm snow sits above a buried weak layer of surface hoar, facets, and a crust. Recently, these slabs have been very reactive to human triggers, surprising riders, and showing wide propagations in moderate to low angle terrain. Moving forward, cold temperatures may decrease the cohesive nature of the slab, but any input of wind or precipitation could easily re-ignite this weak layer.
MONDAY NIGHT - Cold and mostly clear / light north wind / alpine low temperature near -30
TUESDAY - Cold and sunny / light northwest wind / alpine high temperature near -18
WEDNESDAY - Cold with a mix of sun and cloud / light northeast wind / alpine high temperature near -24
THURSDAY - Ongoing cold with a mix of sun and cloud / moderate and increasing northeast wind / alpine high temperature near -26
On Sunday a cornice failure triggered a small (size 1) avalanche 50 cm crown and skiers reported sudden results in test profiles on prominent surface hoar buried 50 cm deep.
On Saturday riders continued to trigger slab avalanches 20-60 cm deep, documented in a handful of MIN reports (Trespass, Mammoth, Spicy, Different Day). Explosives triggered several large (2-2.5) persistent slab avalanches on northerly aspects below 2000 m/
On Friday, there were numerous reports of natural and human triggered persistent slab avalanches up to size 2.5. Some of these were triggered remotely, as outlined in a MIN report that can be viewed here. There were also numerous natural and explosives triggered dry loose, and storm slab avalanches reported up to size 2.
Last week was busy for avalanche activity, on Wednesday (Feb 3) persistent slab avalanche activity really picked up with reports of natural, human, and explosives triggered storm and/or persistent slab avalanches up to size 2 everyday through Saturday (Feb 6).
Many thanks for all of the great MIN reports over the past week!
Recent variable winds have formed slabs in open terrain on a variety of aspects. 20-80 cm recent snow has formed a reactive slab on top of a persistent weak layer that consists of surface hoar, facets, and a crust buried in late January. Below 1600 m a hard melt-freeze crust is underneath 20-40 cm recent snow.
A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which is currently unreactive.
