Regions
Northwest Inland.
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 in the south of the region. On Tuesday, light scattered flurries are expected to continue (2-4mm) with freezing levels at valley bottom and light SW winds in the alpine. Generally dry conditions are expected for Wednesday and Thursday but scattered flurries are possible in some areas. Freezing levels should stay at valley bottom and alpine winds should remain light. The next frontal system is currently forecast to reach the region on Thursday evening. Moderate precipitation is forecast for Friday through to at least Sunday.
Avalanche Summary
No new slab avalanches were reported on Sunday but sluffing from steep terrain was. On Saturday, a skier triggered a size 1 which released down 20-30cm. Natural activity up to size 3 was reported on Thursday and Friday during and following 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. Small avalanches also have the potential to step-down to a deeper weakness.
Snowpack Summary
Prior to the weekend, moderate to locally heavy snowfall and strong southwest winds built deep storm slabs which may still be reactive in wind-exposed terrain. Continued light snowfall is adding to these mature storm slabs or possibly forming new thin storm slabs. About 70cm 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 over 100cm below the surface). This layer has reportedly gained significant strength but I would keep it on my radar, especially in thin-snowpack areas, at higher elevations, and in the far north of the region. Near the base of the snowpack is a crust-facet combination buried in November. This deep persistent weakness was recently reactive and may still be touchy in the far north of the region. Wherever you are, I'd be cautious of this deep and potentially destructive layer. Possible triggers include thin spot triggering in high elevation terrain, a cornice fall, or a smaller avalanche stepping down.
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.
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.