Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Overnight: 10 to 20 cm precipitation forecast, winds strong from the W, freezing levels near 900m.Monday: 10 to 20 cm, winds strong from the W, freezing levels rise to 1200m.Tuesday: Light flurries, moderate to strong winds from the west, freezing levels may rise to 1400m in parts of the forecast area.Wednesday: No precipitation in the forecast, freezing levels continue to rise as high at 1900m in some parts of the forecast area.
Avalanche Summary
There have been reports of easily triggered soft slabs and large surface sluffs in moderately steep terrain, with the slab avalanches propagating quite far. A natural avalanche cycle has been reported throughout the forecast area with avalanches up to size 3. Buried persistent weaknesses may now become reactive with heavy loading from snow and wind.
Snowpack Summary
Some parts of the forecast area have received over 50cm of storm snow, which now overlies a variety of old surfaces ranging from wind slabs, to a soft layer of facetted snow and/or surface hoar from earlier in January now buried in the snowpack between 40 and 60 cm.100cm or more below the surface there is a thin melt freeze crust below 2100m elevation, as well as other buried weak layers (surface hoar, facetted snow, and/or a crust) that continue to be reactive in snowpack tests. There are two deeper layers of note. The late-November persistent weak layer is a sun crust on steep south facing slopes and surface hoar in sheltered areas and now may be180 to 200cm below the surface. The October deep persistent weak layer consists of a layer of facets sitting on a crust at the base of the snowpack. This layer is predominantly found on northerly aspects at tree line and in the alpine. The depth of both these layers makes directly triggering an avalanche on them unlikely (maybe a heavy load on a thin spot in steep terrain), an avalanche stepping down to this layer might dramatically increase the size of the avalanche.
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.