Regions
Northwest Coastal.
Last week's storm snow appears to have stabilized but observations have been limited. A conservative approach is still recommended. The more recent snowfall may be forming new instabilities, especially in wind-loaded features.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Another 3-5mm of precipitation is expected Monday overnight. On Tuesday, light flurries are expected to continue (2-4mm) with freezing levels at valley bottom and light SW winds in the alpine. Light scattered flurries may continue on Wednesday morning but a weak ridge of high pressure is expected to build during the day and should keep things dry through midday Thursday. The next frontal system is currently forecast to reach the region on Thursday afternoon. Moderate-to-heavy precipitation is forecast for Friday through to at least Sunday.
Avalanche Summary
No new avalanches were reported on Sunday. On Saturday, a skier triggered a size 1 which released down 25cm. Natural avalanches to size 2.5 were reported on Thursday and Friday during and after the storm. Skier triggering remains a concern for Monday but natural avalanches are generally not expected. Wind loaded features are my biggest concern for triggering but thin-spot triggering of persistent weakness would have the biggest consequences.
Snowpack Summary
Prior to the weekend, moderate to heavy snowfall and strong southwest winds built deep storm slabs which are expected to be most reactive in wind-exposed terrain. Continued light snowfall is adding to these mature storm slabs or may be forming thin new slabs. About 100cm below the surface, you'll likely find a rain crust which was buried on January 26. Limited observations suggest the overlying slab may have a reasonable bond at this interface. A rain crust and/or surface hoar layer buried mid-January may be found at variable depths (in some areas up to 150cm below the surface). This layer is likely gaining strength, although I would keep it on my radar especially in thin snowpack areas and at higher elevations as it was the bed surface for much of the recent destructive avalanche activity. The November crust/ facet combo near the bottom of the snowpack is thought to be generally well bonded. However, this deep and destructive layer is still reported to be reactive in the far north of the region.
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.