Precipitation combined with a rising freezing level on Monday will create dangerous avalanche conditions. Several large, destructive avalanches have occurred in recent days. Simple terrain, free of overhead hazard is strongly recommended.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Monday
Weather Forecast
MONDAY: Periods of snow, accumulations 20-30cm overnight Sunday through Monday / Moderate to strong southwest wind / Alpine temperature -1 / Freezing level 1500-1700m TUESDAY: Flurries, accumulation 5-10cm / Light to moderate southwest wind / Alpine temperature -3 WEDNESDAY: Flurries / Light southwest wind / Alpine temperature -2
Avalanche Summary
On Sunday several size 1.5 to 2 explosives controlled storm snow avalanches were triggered in the alpine on northeast aspects. Several large and very large avalanches have occurred on weak layers buried deep in the snowpack in recent days (including natural activity up to Size 3), highlighting that dangerous avalanche conditions exist within the region. Explosive control work on Friday and Saturday produced numerous storm slab avalanches Size 2-2.5, as well as several large, destructive Size 3-4, slab avalanches that failed on the mid-December and late-November layers, with crowns from 150-250 cm deep.
Snowpack Summary
About 60-100cm of settled storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects, that was buried mid-January. Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets buried late-November is near the bottom of the snowpack and is now up to 200-250 cm below the surface. All of these layers remain active and have produced recent large, destructive avalanches.
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.