Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Synopsis: Low pressure systems in the north Pacific continues to feed moisture into BC.Tonight: Cloudy with flurries, no serious precipitation expected, freezing level at valley bottom, winds from the west occasionally gusting to moderate.Tuesday: Cloudy with snow, trace to possible 5cm of precipitation, freezing level climbs to 1200 metres, winds from the south west light, gusting to moderate.Wednesday: Cloudy with flurries, possibility of 5 to 10cm of precipitation, freezing level around 900 metres, ridge top winds moderate from the west.Thursday: Cloudy with sunny periods and isolated flurries, 5 to 10cm of precipitation, freezing level around 1000 metres, winds light occasionally gusting to moderate from the west.
Avalanche Summary
A few reports from yesterday of skier accidental and skier controlled as well as some explosive controlled avalanches, in the size 1 to 2 range in the storm snow, mostly wind loaded features above tree line. As well there are reports of sluffing in steep solar affected terrain.
Snowpack Summary
Up to 35 cm of recent storm snow is sitting on a variety of layers. A well developed sun crust has formed on solar aspects and prior to this storm, surface hoar formed on shady, sheltered slopes. At lower elevations, a melt-freeze (or rain) crust can be expected in most areas. Moderate to strong SW winds have formed wind slabs on lee slopesBelow the storm snow, the upper snowpack is generally well settled from the recently warm weather. Two persistent weak layers remain a concern but these problems are becoming more isolated. Before the storm, the early-March crust/facet layer was down roughly 1m and the early Feb layer is down 1.5m or more. These layers are now deep enough that human-triggering is unlikely, but smaller avalanches or cornices failures have the potential to step down to these layers. Freezing levels have been cycling between valley bottom and 1500-2000m, and low elevation terrain saw significant rain last weekend. The snowpack at lower elevations has been generally stable but wet snow or rain may destabilize the upper layers of the snowpack.
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.
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.