Avalanches continue to be triggered by light loads in this region. Forecast warm temperatures are likely to continue this trend.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Saturday
Weather Forecast
Thursday: Flurries. Freezing levels rising to around 1400 m. Ridgetop winds 40-50 km/h from the southwest. Friday: Light precipitation in the afternoon that might fall as rain or snow. Freezing levels between 1800 and 2200 m, ridgetop winds rising to 70 km/h from the southwest. Saturday: light to moderate rain/snow in the 5-10 mm/cm range with freezing levels rising to around 2000 m. strong southwesterly winds.
Avalanche Summary
Numerous natural and human-triggered avalanches were reported to have run during and after the most recent storm, up to and including Tuesday 20th, which is the most up-to-date info at the time of writing. Noteably, those that occurred on Tuesday 20th were larger than those that were reported during the storm, and more likely to have been human-triggered (although natural avalanches were also reported from Tuesday). One very large natural avalanche was reported from an east aspect at 2700 m. We do not have any details about the layer this avalanche ran on. Most avalanches
Snowpack Summary
Between 30 and 50cm of new snow fell during the most recent storm over the weekend. It was distributed by strong winds into deeper, more cohesive deposits in higher wind-exposed terrain. A weak layer that comprises feathery surface hoar crystals up to 15 mm lies directly below the recent storm snow and sits above a crust in many areas, especially on south-facing slopes. This "mid-January" weak layer is widespread and has been the main focus for most of the recent avalanche activity. It has also been consistently producing easy "pop" type failures in snowpack tests.The still problematic mid-December surface hoar/crust layer is now buried anywhere from 60 to 110cm below the surface and continues to produce clean shears at and below treeline. Avalanches were reported to have stepped down to this layer during and after the most recent storm cycle. Although it has become less likely to trigger, I'd continue to treat this layer with respect and suspicion, particularly in the 1700-1900 m elevation band. A release on this layer would have very high consequences.
Problems
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.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.