Several surface hoar layers in the upper snowpack are sensitive to human triggering. A small avalanche could initiate a deeper instability resulting in a large avalanche.Travel in the Alpine is not recommended.
Weather Forecast
Cloud cover for the day with 5-10cm of snow by tonight. Alpine temps could reach -6 with freezing levels staying below 1200m. Winds at ridge top will be 20km/hr gusting to 70km/hr from the south. There will be several storms rolling through our area over the next few days, with up to 40cm of snow by Thursday morning.
Snowpack Summary
40cm of new storm snow sits atop the January 16 surface hoar layer which is settling quickly and reactive in tests. Previous strong south winds have built pockets of wind slab in the Alpine. The December 15 surface hoar is down 100cm and is highly visible in profiles and still producing sudden planar results in tests.
Avalanche Summary
Several natural avalanches size 2-3.5 came down the north aspect of Mt. Macdonald this morning. The size 3.5 dusted and spread woody debris on the highway for a 100m section. Two sz 2.5 were observed yesterday from the same area originating from steep, rocky terrain.Avalanches originating in the Alpine have the potential to run into valley bottoms.
Confidence
Timing, track, or intensity of incoming weather system is uncertain on Sunday
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.