Avoid all avalanche terrain and overhead hazard as conditions will continue to deteriorate Monday.
A few buried surface hoar layers and dense snow make conditions spicy!
A weak layer of surface hoar, now about 45-80 cm deep, may be possible to trigger on sheltered, shaded slopes near treeline (above 1700 m). Recent activity on this layer has been most notable in the southern half of the region.
Touchy storm slab conditions exist in all steep terrain and at all elevations. A couple of buried surface hoar layers in the top 50 cm will be very reactive anywhere slab properties develop due to wind or warm temperatures.
A stalled offshore low continues to push bands of warm air, wind and precipitation our way in the upcoming days with clearing mid-week.
Sunday night: Snow, 10-20 cm, moderate south ridge wind, alpine low temperatures around -3 C. Freezing level 1000 - 1300 m.
Monday: Snow, 10-20 cm, moderate southwest wind gusting strong, alpine high temperatures around -1C. Freezing level 900-1600 m.
Tuesday: Snow, 5 - 20 cm, moderate to strong southwest wind, alpine high temperatures around -4C. Freezing level 900-1500 m.
Wednesday: Cloudy with sunny breaks and isolated flurries, trace to 5 cm new snow, light west ridge wind gusting moderate, alpine high temperatures around -4C. Freezing level 600-900 m.
We anticipate a widespread avalanche cycle is ongoing in zones that received heavy snowfall and wind on Sunday. Early reports from Sunday indicate touchy skier triggered (size 1-1.5) avalanches that failed on surface hoar at treeline and below treeline where temperatures warmed snow into slabs. Explosive triggered small and large (size 1-2) avalanches were widespread on wind loaded lee alpine aspects (NE - NW).
On Thursday, there were reports of touchy conditions and a widespread avalanche cycle including numerous skier triggered small avalanches (size 1-1.5) and a few larger skier triggered and natural avalanches (size 2-2.5). Last week a couple persistent slab avalanche (size 1.5) were triggered in the Valhallas on the early January surface hoar layer on steep north treeline terrain.
An additional 15-25 cm of snow is forecast overnight Sunday into Monday. This adds to the highly variable previous snowfall amounts of 5-35 cm. It's all coming with warming temperatures and moderate south wind; and it buried a surface hoar layer on Friday night. Expect very touchy avalanche conditions in heavier snowfall zones, particularly where buried surface hoar is present or where wind has transported snow into wind slabs.
There are a series of surface hoar layers in the top meter of the snowpack that could result in surprisingly large avalanches. The first from Friday night (down 20-50 cm), a second more widespread and unstable layer from the long drought (down 30 - 70) and a much deeper layer from early January (down 40 - 130). This last layer was showing only isolated reactivity in shallow snowpacks in the Valhallas and southern Selkirk's.
Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable. The first is from December consisting of decomposing surface hoar and a crust (buried 100-15cm) and the second from early November consisting of a series of crusts with faceted snow (closer to the ground).
