Choose conservative terrain this weekend as storm snow continues to show reactivity.
Avoid wind loaded features, and watch for strong sunshine affecting south facing slopes - reactivity will increase if skies clear.
Check out the latest Forecaster Blog for the latest on the Deep Persistent Slab Problem.
Recent storm snow has been affected by southwest winds, which have now switched to east. Expect deeper wind affected deposits on all aspects, while sheltered terrain may still produce loose dry avalanches - be prepared to manage your sluff.
Additionally areas that see clear skies and strong sun should avoid sun affected slopes. Surface snow may rapidly lose cohesion.
Buried weak layers of surface hoar and facets have shown reactivity, and are capable of producing large avalanches.
Manage your terrain choices to minimize exposure to this problem. Avoid large open slopes were avalanches can propagate widely, and be cautious around sheltered terrain features where surface hoar may persist especially convex rolls.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth, but storm slab avalanches in motion have the potential to step down and produce very large avalanches with wide propagation. Suspect terrain for human triggering includes steep, shallow and rocky terrain.
Avalanche activity has continued throughout the week, as storm snow kept stacking up. Activity included storm slabs, wind slabs in wind loaded features and loose dry avalanches from steep sheltered terrain.
Natural and human triggered avalanches continue to be reported, mostly to size 2. Most avalanche activity is isolated to the storm snow or old/new interface, while several larger natural slab avalanches were reported to size 3.5 likely failing on the buried facets and surface hoar layers.
Deep persistent slab avalanche reports continue to trickle in over the week, to size 3. This evidence indicates the low probability but very high consequence weak basal snowpack is still active. Avalanches have occurred on all aspects and generally between 2200 m and 2800 m in elevation. Reports commonly noted the variation in depth - indicating that areas where the snowpack is shallow and rocky, or where it varies from thick to thin rapidly are still to be avoided. A fatal size 3 avalanche occurred near Invermere on Wednesday, which is directly adjacent to this forecast region.
Storm snow from this week has been redistributed by recent southwest winds into deeper deposits on north and east facing aspects. Current easterly winds are expected to build deposits on west facing slopes as well, resulting in variable wind loading patterns. This storm snow sits over wind effected surfaces, a thin sun crust on steep south facing slopes.
Around 50-90 cm deep a layer of small surface hoar exists in lower elevation sheltered areas. Elsewhere heavily wind effected surfaces exist, with faceted (sugary) snow from the late February Arctic blast.
Another small layer of surface hoar is buried 70-130 cm deep from mid February. This layer is most likely found around treeline elevations in areas sheltered from the wind. These two layers have shown reactivity, producing avalanches and concerning test results. The remainder of the mid-snowpack is generally strong.
A layer of large and weak facets that formed in November is deeply buried. Found near the base of the snowpack it is very slow to gain strength. The likelihood of human triggering this layer is currently low given its depth. However deep persistent slab avalanches continue to occurr, confirming it is still best to avoid steep, thin and rocky slopes at alpine and upper treeline elevations.
Saturday Night
Light southeast winds, gusting moderate. Freezing levels below valley bottom.
Sunday
Mostly sunny, especially in the north, with cloudy periods elsewhere. Moderate southeast winds ease over the day Freezing levels below 500 m, alpine high of -8 °C.
Monday
A mix of sun and cloud. Light southerly winds. Freezing levels around 800 m in the south, alpine high of -5 °C. Light snowfall possible in the afternoon.
Tuesday
Mostly cloudy with moderate southwest winds. Freezing levels rise to 1000 m. Alpine high temperature of -3 °C. Flurries in most areas.
More details can be found in the Mountain Weather Forecast.
