A big change in the weather is headed our way. Tuesday is the probably going to be the last day you can confidently get after it in big terrain for a while.
Confidence
Poor - Due to the number of field observations
Weather Forecast
Bottom Line: The weather is changing, the inversion should be cleared out by Tuesday morning. The coast will likely get hammered as a digging upper trough makes landfall over the next few days. Some of the snow and southerly winds associated with this event are expected to spill over into the Purcells. At this point amounts and timing are too dynamic to pin down, but the region should see 1 to 3cm of snow Tuesday night, with an additional skiff of snow Wednesday. Strong SW winds are expected throughout the region beginning Tuesday night. The freezing level should remain at valley bottom through Tuesday night. Its expected to climb to around 1500m Wednesday before returning to valley bottom Wednesday night. The pattern looks similar for Thursday with the freezing level once again rising to around 1500m. For detailed mountain weather information visit: avalanche.ca/weather.
Avalanche Summary
The only recent avalanche activity reported has been loose snow sluffing from steep north facing terrain.
Snowpack Summary
The snowpack is extremely variable at this time. Wind scoured north facing slopes exist at treeline and above from the recent strong winds associated with the arctic front. South facing slopes have wind slabs at tree line and above and may be hiding surface hoar from the previous spell of cold clear weather. Surface facetting has been observed in the region as a result of the recent cold weather and clear skies, and surface hoar up to 20mm has been reported in sheltered locations below treeline. There are a number of surface hoar layers now buried in the snowpack, but at present they appear to be unreactive, the most recent having been buried on Nov 24th. In shallow snowpack areas, especially on northern aspects, there may be a weak facetted layer at the base of the snowpack. Recent warming at upper elevations has likely changed the snowpack on all aspects, especially those facing south where you can expect a suncrust above 1500m.
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.