Touchy avalanche conditions exist from all the recent snowfall. Use a cautious approach in the mountains this weekend.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The last of the Pacific storm pulses is expected to hit the region Saturday overnight. Around 10cm of snowfall is expected with freezing levels around 1200m. Light scattered snowfall may continue through the day on Sunday. Alpine winds are expected be strong from the SW in the morning but will ease in the afternoon. Monday is expected to be dry with a mix of sun and cloud. Freezing levels are forecast to drop to near valley bottom and alpine winds should be light from the NW. Tuesday looks to be similar with mainly dry condition and a mix of sun and cloud.
Avalanche Summary
Reports from Thursday include a remotely triggered Size 1.5 slab avalanche from a snowmobiler on a sheltered north facing slope below treeline that ran on surface hoar buried early-December. On Friday, ski cutting produced size 1 soft slabs in immediate lee features (generally north through east aspects).
Snowpack Summary
Continued snowfall brings total treeline snowpack depths to over 1m, with even more in the alpine, but it diminishes quickly below around 1700m. Recent rain created a near surface crust as high as 1800m (or higher in the southern part of the region). Above that elevation, storm and wind slabs are bonding poorly to the old snow surface buried early December, which is probably a crust and/or a combination of facets and buried surface hoar now down around 40-60cm in sheltered treeline areas. The buried surface hoar may be well preserved in sheltered areas, creating particularly touchy slabs with the potential for remote triggering, extensive releases and prolonged sensitivity to triggering. Below that a thick weak layer of facets may be lurking around the thick mid-November crust.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.