Keep terrain selection conservative as storm snow accumulates on Sunday. Avoid avalanche terrain and overhead hazard during heavy snowfall.
Small avalanches may step down to deeper instabilities, most likely on sheltered north facing slopes.
Persistent slab avalanches are possible on shaded aspects due to two buried layers of surface hoar. Various combinations of crusts above and below these layers has made the distribution of this problem spotty.
Be cautious on steep open slopes at treeline, especially in terrain where surface hoar is more likely to be preserved - like cut blocks.
Fresh and reactive storm slabs will build overnight and into Sunday. Expect greater sensitivity in wind loaded areas, around ridgelines on easterly facing slopes.
SATURDAY NIGHT: 5-10cm of snow possible overnight, heaviest in the east near Nelson. Light westerly winds. Freezing level around 1200 m dropping to valley bottom.
SUNDAY: Mostly cloudy with snowfall continuing over the day. 10-20 cm is forecast, again heaviest near Nelson. Light northwest winds. Freezing levels around 1200 m. Alpine high of -6.
MONDAY: Mix of sun and cloud, light winds from the north. Chance of isolated flurries. Freezing levels at valley bottom. Alpine high of -10.
TUESDAY: Mostly clear skies with moderate northeast winds. Freezing levels at valley bottom, alpine high of -12.
There have been regular reports of small natural and human-triggered wind slabs along ridgetops over the past few days. With the incoming storm we expect to see larger slabs forming at upper elevations.
Persistent slab avalanches were reported on Friday from explosive and human triggers, failing on the late January surface hoar layer. This activity was limited to north/northeast aspects around tree line elevations - these specific areas continue to be a concern for human triggering throughout this storm.
New snow will form reactive storm slabs at all elevations. The storm snow will bury a small surface hoar layer in sheltered terrain - which sits over a melt freeze crust on solar aspects at all elevations, and wind effected surfaces in exposed terrain.
Two layers of buried surface hoar sit in the upper snowpack, most likely to be found and triggered on north aspects in sheltered areas. These are now down around 30-50 cm and 60-80 cm deep. These layers remain reactive in some snowpack tests and have resulted in avalanche activity over the past week.
The lower snowpack is well consolidated, with a crust/facet layer found 100 to 200 cm deep. It is currently considered dormant, but could become active later this season. Check out the forecaster blog for more information.
