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. Strong NW winds easing. Freezing level around 1200 m, dropping to 300 m overnight.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 winds. Freezing level around 1700 m.
Avalanche Summary
A natural avalanche cycle to size 2.5 occurred on Wednesday in response to storm loading on all aspects in the alpine. Skiers triggered several size 1-2 wind slabs on N to NE aspects on Thursday. Many of these failed at the base of the recent storm snow on crust interfaces. Some observers mentioned solar-triggered avalanches as well.
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 or so of the snowpack, mainly on high-elevation northerly aspects. It may be slowly gaining some strength, but these slopes should still 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.