Strong winds, heavy snowfall, and rising temperatures have resulted in HIGH avalanche danger.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Heavy snow and strong Southerly winds overnight, Friday morning, and Friday afternoon. Freezing levels climbing up to about 1800 metres in the North and east of the region, and closer to 2000 metres in the West and South of the region. Strong Southerly winds continuing on Saturday morning. Freezing levels dropping to 1400 metres on Saturday afternoon as the winds slow to moderate Southwest. Light Southerly winds combined with light precipitation and cooler temperatures on Sunday.
Avalanche Summary
Several natural avalanches up to size 2.0 were reported on Wednesday that released within the storm snow down 20-30 cm. Heavy loading from new snow and wind on Thursday is expected to have resulted in a storm slab cycle on the late January crust or on a change within the storm snow about 10-15 cm above the crust. Forecast strong winds and heavy snow are expected to increase avalanche size and avalanche frequency as the storm continues.
Snowpack Summary
Thin new slabs may not be bonding well within the storm snow. Pockets of wind transported snow at ridgetops may be easy to trigger where they are sitting on the crust that formed last week. The new storm slab is up to 40 cm thick and sits above a variety of old surfaces. The old surfaces include the crust that formed last week, a new layer of surface hoar that developed during the clear weather late last week, and in some places wind slabs that developed smooth hard surfaces. Deeper in the snowpack the mid-January surface hoar remains a concern. It can be found down 60-120 cm across the region, but in most places it is about one metre down. In some locations it has reportedly gained quite a bit of strength, but elsewhere it is still producing sudden collapse (popping) failures in snowpack tests. The mid-December surface hoar layer is now 80 to 140cm below the surface and has become unlikely to fail, the storm at the end of the week should be a good test to see if it will become active again.
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.
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.