New wind slabs are expected to be touchy on Monday, especially where they overlies surface hoar or a crust. Loose dry avalanches should be expected on steep slopes.
The storm snow is expected to form new wind slabs in exposed terrain. These will be touchy where the new snow overlies surface hoar or a crust.
A concerning weak layer of faceted grains above a melt-freeze crust is around 100 to 150 cm deep, which has produced large avalanches. This problem has been less active recently, but we have been reminded multiple times in the last month that this layer could remain a concern all winter. Thin rocky start zones are the most likely place to trigger this layer. Snow loading from new snow and/or wind, daytime warming, cornice falls, and step-downs from smaller avalanches could increase the chance of an avalanche on this layer. Learn more about this crust and how to deal with it in this forecasters' blog.
A storm system brings snowfall to the region Sunday night and is expected to linger through part of the day on Monday. Modelled snowfall amounts and timing are highly variable which is creating a lot of uncertainty for conditions on Monday.
Sunday Night: Snowfall 10-15 cm, moderate to strong SW wind, treeline temperature -5 C°.
Monday: Snowfall 5-10 cm, moderate SW wind, treeline high around -6 C°.
Tuesday: Unsettled with snow flurries and sunny breaks both possible, light variable wind, treeline high around -12 C°.
Wednesday: Mainly sunny, light variable wind, treeline high around -15 C°.
No recent avalanches have been reported in the last few days.
The last report of deep persistent slab avalanches is from January 21, when some very large avalanches were triggered by cornice falls and wind slab avalanches. Although deep persistent slab activity has recently tapered, it could still be possible to trigger large avalanches in steep, rocky terrain.
The new snow will bury heavily wind affected snow surfaces in exposed terrain, a melt-freeze crust at low elevations and on solar aspects extending into the alpine, and surface hoar in sheltered terrain. The January 18 melt-freeze crust extends up to around 2000 m elevation and can be found down around 20 cm.
The primary persistent layer of concern in the snowpack is a crust that formed in early December and is now 100-200 cm deep. This layer is found most areas through the region, but with varying test results. Recently, the layer has shown more reactivity in shallow snowpack areas.
