The recent storm snow is expected to be touchy on Tuesday and storm slabs are likely primed for human-triggering, especially in wind-loaded terrain. Conservative terrain selection is essential.
Extra caution is also advised around steep sun-exposed slopes in the afternoon if the sun is shining brightly.
Recent observations show older persistent weak layers in the snowpack may still be reactive and storm slab avalanches in motion have the potential to step down to deeper layers resulting in larger and more destructive avalanches.
The recent storm snow sits over a weak layer that formed during the recent period of very cold temperatures and is expected to remain very reactive to human triggering, especially in wind-loaded terrain.
On Sunday, a natural size 2.5 storm slab was observed in the south of the region at 1200 m which is expected to have failed on the weak layer of facets and surface hoar below the recent storm snow. A controlled size 2 storm slab was also reported which was 50 cm thick. In the north, a couple of natural size 1.5 storm slab avalanches were reported.
This MIN report from Saturday near Terrace includes reports of numerous small storm slab avalanches but also shows an avalanche stepping down to an older weak layer.
This MIN report from Sunday has a great photo showing the temperature inversion and the effect of the recent warm temperatures. As temperatures cool, a new surface crust can be expected at elevations that saw the recent warm air and/or rainfall.
The recent storm snow has buried a highly variable snow surface that had formed during the recent period of extended cold temperatures and outflow winds. This newly buried weak layer consists of widespread facets, patchy surface hoar in sheltered terrain, and heavily wind-affected surfaces in exposed terrain including wind-scoured and wind-pressed surfaces, old hard wind slabs, and sastrugi.
A layer of large surface hoar crystals, buried in early December, was found down 20 to 50 cm prior to the storm. This layer has previously produced small but remotely-triggered avalanches.
The lower snowpack is well consolidated below a crust that had formed in mid-November which can be found below around 1200 m elevation.
Both the early-December surface hoar and mid-November crust have been dormant recently but could wake up with the new load from the storm snow, and avalanches have the potential to step down to these deeper layers.
Monday night
Snowfall 10-20 cm, moderate to strong SW wind, freezing level around 1000 m.
Tuesday
Mainly cloudy in the morning, sunny breaks in the afternoon, light to moderate NE wind, freezing levels generally falling to around 500 m or lower.
Wednesday
Mainly cloudy with a chance of light flurries, light to moderate SW wind, treeline high around -3 °C.
Thursday
Cloudy with light snow, moderate to strong SE-S wind, treeline high around -5 °C.
More details can be found in the Mountain Weather Forecast.
