A warm, wet and windy storm is ramping up avalanche danger throughout the region. Expect avalanche problems to be increasing over the course of the day on Friday.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
Thursday night: Flurries bringing 5-10 cm of new snow. Moderate to strong southeast winds.Friday: Continuing flurries bringing 10 -15 cm of new snow over the day. Moderate south winds. Freezing level to 1400 metres with alpine temperatures of -3.Saturday: Continuing flurries bringing up to 5 cm of new snow. Light southwest winds. Freezing level to 1100 metres with alpine temperatures of -6.Sunday: Mainly cloudy with isolated flurries and a trace of new snow, intensifying in the evening. Light southeast winds. Freezing level to 1300 metres with alpine temperatures of -4.
Avalanche Summary
Recent reports show observations of both natural and human triggered wind slab avalanches running to Size 1.5 in alpine and tree line lee terrain. On Friday, ongoing storm slab formation will lead to easy human triggering at the depth of new snow as well as the potential for natural avalanche activity. At upper elevations, the deeper mid-February weak layer has been trending toward a low likelihood of triggering. However, with new snow and wind loading the snowpack, it would be best to consider the potential for reactivity at this layer in your terrain selection.
Snowpack Summary
After 25 cm of new snow blanketed the region on Wednesday night, roughly 35-40 cm of new snow lies over a crust that formed over last week's storm snow. This crust exists at about 2000 metres and lower. Beneath the previous storm snow, an older rain crust that formed last week is now buried about 55-75cm deep. The mid-February crust/facet layer can still be found at the upper end of treeline and into the alpine. This interface is now 100-140 cm deep and may be over 200 cm deep in wind loaded terrain. Although there is growing uncertainty about how much longer it will remain reactive, continued caution is warranted as new snow and wind continue to load the upper snowpack and stress deeper layers.
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.
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.