Confidence
Fair - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Synopsis: High pressure at the surface and aloft should result in a classic spring pattern. Freezing levels are expected to rise above treeline each day, dropping almost to valley bottom overnight. Winds should back way off, only light values are expected even at ridgetop through the weekend.Friday: Freezing Level: 1500m rising to 2000m; Precipitation: 0:2mm - 1:3cm; Wind: Treeline: Light, SW | Ridgetop: Moderate, W/NWSaturday: Freezing Level: Valley Bottom rising to 1700m; Precipitation: 0:2mm - 1:3cm; Wind: Treeline: Light, NE | Ridgetop: Light, NWSunday: Freezing Level: Valley Bottom rising to 2000m; Precipitation: Nil; Wind: Treeline: Light, N | Ridgetop: Light, NW
Avalanche Summary
Lots of loose wet activity to size 2 on all aspects between 1700 and 1900m Wednesday. Some natural wind slabs ran naturally to size 2 on NE and E facing features at 2500m too.
Snowpack Summary
Warm temperatures resulted in the freezing level reaching to almost 2400m early this week in the southern Purcells, around 1800m in the north. This has helped to settle out last weeks storm snow, it's reported to be bonding well to the old surface. Strong winds out of both the SW and NW have redistributed what little dry snow still exists at upper treeline and alpine elevations into wind slabs that are most prevalent immediately lee of ridge crest Three persistent weak layers exist in the highly variable snowpack of the Purcells:The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human triggering, but still has the capacity to produce large avalanches.The mid-February crust/facet/surface hoar combo is typically down 60 - 120cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up, which would result in very large and destructive avalanches.Weak basal facets exist in many areas, but triggering is unlikely.
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.
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.