The weekend's storm instabilities are expected to linger for a few days.Use extra caution on steep south-facing slopes during the afternoon if the sun is out in full force.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
A ridge of high pressure will bring dry and mostly sunny conditions on Monday. Freezing levels are expected to be around 1000m in the afternoon and ridgetop winds should be light from the north. A mix of sun and cloud is expected for Tuesday with freezing levels falling to valley bottom and light alpine winds from the NW. Light snowfall is being forecast for Wednesday.
Avalanche Summary
On Friday, ski cutting produced size 1 soft slabs in immediate lee features (generally north through east aspects). On Saturday, explosives and ski cutting produced storm slabs size 1-2 which were typically 20-60cm thick. On Sunday, explosives triggered a few size 2 wind slabs which were typically 30cm thick.
Snowpack Summary
The series of storms last week produced 70-90cm of new snow in the region. A rain crust which formed during the middle of the storm is now down 40-60cm and has become the primary layer of concern during the weekend storm. The early December interface consists of crust, surface hoar, and/or facets and is typically down 70-90cm. Around 20-30cm below this interface is a rain crust from mid-Nov with a thick layer of facets below it. Both the early-Dec and mid-Nov layers have become dormant and are likely being capped at treeline and below by the more recent rain crust layer. However, these layers may still be reactive to heavy triggers such as cornices, explosives, or smaller avalanches stepping down.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.