Fresh storm slabs may be reactive to skier and rider triggering on Saturday. A persistent weak layer of surface hoar, facets and a crust is buried 30-60 cm down. This avalanche problem is less obvious and harder to predict, so conservative terrain choices are best.
30-60 cm sits above a buried weak interface that consists of surface hoar, facets, and/ or a crust. Forecast snow and strong wind may create enough cohesion and load to these weak layers resulting in a reactive persistent slab problem just waiting for a skier or rider to trigger.
10-25 cm of new, low-density storm snow has slowly accumulated over the past two days. Changing wind directions may deposit deeper and stiffer slabs on multiple aspects. I suspect that anywhere the new snow feels stiff and more cohesive that the slab may be more reactive, especially where it sits above a buried weak layer.
Loose-dry avalanches may be seen from steeper slopes where there is little cohesion in the recent storm snow.
An arctic front gradually pushes its way South bringing cold air and some light embedded flurries. A cold northwest wind will persist through the forecast period.
Saturday: Cloudy with flurries 5-10 cm. Alpine temperatures near -12 and light wind from the southeast.
Sunday: Mix of sun and cloud. Alpine temperatures near -20 with light ridgetop wind from the northwest.
Monday: A mix of sun and cloud. Alpine temperatures near -25 and mostly light wind from the northwest.
On Thursday a MIN report from the Seaton South Ridge triggered a size 1 wind slab on a north aspect at treeline. The report said that the bed surface had a few cm's of soft snow possibly surface hoar above a somewhat icy crust. The slab was small but ran fast on the bed surface. Awesome report! Thanks for sharing this information. I suspect that once this new low-density storm snow forms more of a slab, conditions may increase in reactivity and hazard. Skier and rider triggering is likely.
Up to 10-25 cm of new snow fell by Friday bringing 25-50 cm of accumulative low-density storm snow from the past week over a variety of old snow surfaces. These old surfaces include surface hoar in locations sheltered from the wind at all elevations, surface facets, and stiff wind affected snow. On solar aspects, a buried sun crust can be found and a thick crust exists near the surface below 1000 m. Additional snow and changing wind combined with cohesion may stress these potentially weak interfaces, creating the persistent slab problem.
The lower snowpack has two decomposing crust layers. The upper crust is 70-140 cm deep and continues to show occasional hard sudden results in snow pits. The deeper crust at the bottom of the snowpack is more prevalent in shallow snowpack ranges. These deep persistent layers seem to be dormant under the current conditions, but shallow rocky slopes should still be carefully assessed and approached with caution.
