Warm temperatures on Sunday will make higher elevations a lot more enticing than lower down, potentially drawing you into more places where wind slab formation is ongoing. Keep seeking sheltered spots! Triggering a wind slab right now is probably the most effective way to cause a large and destructive step-down avalanche.
In all exposed areas, new snow and strong southwesterly winds are building deep pockets in lees that are reactive to natural and human triggers. Avoid lee and cross-loaded slopes.
If triggered wind slab avalanches may step-down to deeper weak layers and initiate large and destructive avalanches.
Warm temperatures and rain to a possible 1500 metres will promote wet loose avalanche activity in steep terrain at lower elevations as surface layers lose cohesion.
A layer of large, weak facets sits near the base of the snowpack. This layer is most prominent in upper treeline and lower alpine elevations. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain. This layer has recently produced very large natural avalanches see avalanche summary for more information. Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.
Recent observations have shown a trend away from very large persistent slab and deep persistent slab avalanches and toward surface instabilities such as wind slabs. We expect this trend to continue, however the basal snowpack remains questionable and should still figure into terrain selection around steep features with shallow or variable snowpack areas where these layers may be more easily triggered by a person or machine as well as large wind slab or cornice releases.
As recently as last week, very large natural avalanches were observed failing on deep snowpack layers. Two were size 3 persistent slab avalanches on steep north-facing aspects with 750 m wide crowns. A size 3.5-4 deep persistent slab avalanche was also observed. It is suspected this avalanche failed in depth hoar at the base of the snowpack.
15-20 cm of new snow should accumulate in the region by end of day Sunday, adding to roughly 80 to 130 cm of recent storm snow from steady stormy weather over the past week. This storm snow is reportedly forming a good bond with previously wind-affected surfaces as well as the late January melt-freeze crust found on sun-exposed slopes and on all aspects below about 1600 m.
Several strengthening crust/facet/surface hoar layers can still be found in the upper and middle portions of the snowpack. The most concerning persistent weak layer, however, is at the base of the snowpack and composed of large and weak facets formed in November. This layer is widespread and most likely to be triggered in steep, rocky alpine and upper treeline terrain.
Saturday night
Cloudy with flurries bringing about 5 cm of new snow. Strong southwest winds.
Sunday
Cloudy with increasing snowfall bringing 10-15 cm of new snow to higher elevations, light rain below 1500 metres. Continuing overnight with snow at most elevations. Strong to extreme southwest winds. Treeline high temperatures around 0 with freezing levels rising to 1700-1800 metres.
Monday
Cloudy with easing flurries bringing 15-25 cm of new snow, including overnight amounts. Light to moderate southwest winds shifting west. Treeline high temperatures around -7.
Tuesday
Mainly cloudy with isolated flurries. Light northwest winds shfting southwest. Treeline high temperatures around -8
More details can be found in the Mountain Weather Forecast.
