A big rise in temperatures may mean that the deep persistent slab rears its ugly head again. Much uncertainty exists as to what this layer will do as temperatures climb. High levels of uncertainty are best managed with conservative terrain selection.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Freezing levels and alpine temperatures are difficult to forecast in the coming days with mild temperatures and temperature inversions dominating the weather pattern this weekend.THURSDAY NIGHT - Mainly cloudy / southwest winds, 10-20 km/h / alpine low temperature near -5 / freezing level 1100 m / alpine temperature inversionFRIDAY - Mainly cloudy / southwest winds, 10-30 km/h / alpine high temperature near +2 / Freezing level 1500 m / alpine temperature inversionSATURDAY - A mix of sun and cloud / southwest winds, 20 km/h / alpine high temperature near +5 / freezing level 3000 m / alpine temperature inversionSUNDAY - Sunny with cloudy periods / southwest winds, 20-30 km/h / alpine high temperature near +6 / freezing level 3000 m / alpine temperature inversion
Avalanche Summary
A few size 1 natural and explosives triggered avalanches were reported in the region on Thursday.
Snowpack Summary
10-20 cm of recent storm snow has been redistributed by strong winds and has formed wind slabs at upper elevation. This new snow sits on previous hard wind slabs, a scoured and shallow snowpack on exposed ridges, and soft snow in sheltered areas. Below 1200 m, expect to find a crust at or near the snow surface.Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks. Warming temperatures and sunshine over the coming days could re-activate this layer, resulting in a possible avalanche cycle.
Problems
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.
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.