A Special Avalanche Warning applies to the south of the region.Extra caution is required over the next few days as the alpine warms. Storm slabs are expected to remain reactive on Monday, especially in wind loaded terrain and on sun exposed slopes.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Monday
Weather Forecast
A ridge of high pressure is forecast to keep the region dry until Wednesday. On Monday, mostly sunny conditions are expected with light to moderate alpine wind from the northwest. Freezing levels are forecast to climb to around 2000 m or so by Monday afternoon. On Tuesday, sunny conditions are expected with the potential for valley fog to develop. Alpine wind is forecast to be light to moderate from the southwest. Freezing levels are forecast to reach as high as 3000 m and a temperature inversion will likely develop. A weak storm pulse is expected to reach the region sometime on Wednesday. Freezing levels are forecast to remain above 2500 m and high elevation rain is expected.
Avalanche Summary
On Saturday, reported natural activity was limited to one size 2 wind slab on a northeast aspect at 2600 m elevation. A couple size 2-2.5 storm slab avalanches were remotely triggered from up to 100 m away. Explosives also triggered numerous size 2-3 storm slabs. These slabs were typically 40-80 cm thick. On Friday, natural and human triggered storm slab avalanches up to size 3 were reported. In the mountains west of Invermere, explosives triggered four persistent and deep persistent slab avalanches. This activity was on east and southeast aspects and released 1.5-2.5 m deep. On Monday, the recent storm snow is expected to remain reactive to human triggering, especially in wind affected terrain. Persistent slab avalanches are a concern, especially in the thinner snowpack areas along the eastern side of the range. Extra caution is recommended during the heat of the afternoon, especially on sun exposed slopes. This will become increasingly important through the week as freezing levels remain very high. We are entering the first period of substantial warming following months of sustained cold conditions. Any weaknesses lingering in the snowpack will be tested in the coming days.
Snowpack Summary
40-60 cm of storm snow has typically accumulated of the past few days. Recent strong winds from the south and west have redistributed this snow in exposed terrain forming touchy wind slabs. Weaknesses exist within this recent storm snow with reports of 'upside-down' conditions and easy shears within the top 60 cm. The early February interface is now down 60-80 cm and includes sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. A persistent weakness buried mid January is now down 80-150 cm and consists of buried surface hoar in sheltered areas, sun crust on south aspects, and/or faceted old snow. This and deeper persistent weaknesses remain concerns isolated to shallow snowpack areas where they lie closer to the surface. These layers are expected to get tested with the upcoming period of sustained warming, and if they wake up, very large avalanches are possible.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.