Snowfall amounts for Friday night are uncertain. Danger could spike to HIGH by Saturday if we get more than forecast.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
Saturday: Overnight snowfall tapering off to a cool and unsettled flow with light snow. Moderate W winds. Freezing level around 1000 m.Sunday: Cold and unstable weather, with light snow. Light N winds. Freezing level around 1000 m.Monday: Cold and unstable weather, with light snow. Light or calm winds. Freezing level around 1500 m.
Avalanche Summary
Observations have been limited during Wednesday’s storm, when a natural avalanche cycle is expected to have occurred. On Thursday, a cornice fall triggered a size 2.5 slab. Skiers also triggered size 1 slabs. These events were on NE aspects above 2300 m.
Snowpack Summary
Snowfall on Friday night is expected to create new storm/wind slabs, especially near ridge top. This will add to existing storm slab and wind slab problems at alpine and treeline elevations. A surface hoar interface is buried within the upper metre of the snowpack, mainly on high-elevation northerly aspects. It is still producing moderate, sudden results in snowpack tests, and these slopes should be treated with suspicion. On other slopes, recent storm snow overlies a crust, with a variable bond. At low elevations, previously rain-soaked snow is likely to now be refrozen and strong.
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.