Confidence
Fair - Freezing levels are uncertain on Saturday
Weather Forecast
A surface ridge moves into the region Friday keeping the area dry while northwesterly flow aloft keeps scattered clouds in place. Ridgetop winds will be at strong values out of the W near ridgetop Friday & temps will remain cool; Expect a daytime High of -5 and an overnight Low of -10 @ 1500 m. Things begin to change a bit Saturday as the ridge breaks down allowing moist flow in from the pacific. The first storm associated with the new pattern enters the region Saturday night, sticking around through Sunday. Freezing levels are expected to rise to 1300 m Saturday night and the region should 5 -10 cm over the weekend.
Avalanche Summary
Our field team was out in the region Thursday investigating a slide that ran full path. This avalanche path has a SE facing start zone that had been crossloaded by the recent westerly winds. A wind pillow failed high on the slope triggering a size 3 avalanche with a crown as deep as 85 cm. The likely culprit is a crust/facet combo from mid-December.
Snowpack Summary
Last week 40-60cm of snow formed soft slabs over a crust/facet/surface hoar combo which has settled remarkably quickly. Deeper in the snowpack, a surface hoar layer buried in early December remains a concern, as avalanches triggered on this layer would be destructive. There may have been releases on this layer post storm but at this time nothing has been reported. It should be noted that basal facets exist in many parts of the region too. Facets sandwiched between two firm layers in the top metre of the snowpack are being monitored in the south-east.
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.
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.