Snowfall amounts are highly variable. In some parts of the region, danger may be HIGH in the alpine.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Snow eases to light amounts on Monday, then the next pulse begins on Monday night, bringing around 5-15 cm snow with moderate to strong SW to NW winds. Freezing levels peak around 2200 m on Monday afternoon, then drop on Tuesday to around 1500 m.
Avalanche Summary
A natural avalanche cycle, size 2-3, was observed on Friday and Saturday. These were slabs up to 100 cm deep and loose wet avalanches on all aspects.
Snowpack Summary
Strong winds have shifted snow onto lee slopes at high elevations. Cornices are large and fragile. Rain below treeline is saturating the snowpack. In the alpine and at treeline, two persistent weak layers in the upper metre or so of the snowpack are the main story. The mid-March layer, around 60 cm down, is most reactive where it exists as a crust. Around 80-100 cm down, the mid-February facet/crust interface has also been reactive. Both layers (or facets in between the two layers) are sensitive to triggering and propagate easily, causing very large avalanches. As temperatures rise on Monday, the reactivity of storm slabs and persistent slabs may go up.
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.