Regions
Northwest Inland.
The last system dumped more snow than forecast to parts of the region. If this pattern continues expect periods of HIGH avalanche danger over the next few days.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Synopsis: We could see a short lull in the weather on Thursday before another strong frontal system hits the North Coast on Friday. Expect 5-10 cm (mm) tonight and Thursday followed by 15-25 cm (mm) on Friday. The freezing level should be around 1600 m and winds are strong from the southwest. Saturday looks like another lull in intensity but we could still see 5-15 cm with a freezing level a couple hundred metres lower.
Avalanche Summary
Periods of heavy snow or rain, strong ridge winds, and warming will probably tip off a natural avalanche cycle in parts of the region. We could see wet activity at lower elevations with storm/wind slabs where snow accumulates. There is also potential for deep persistent weaknesses to be overloaded producing isolated very large and deep slides. This pattern should continue for most of the week.
Snowpack Summary
Periods of heavy snow (or rain at lower elevations) and strong southerly ridge winds are building deep and dense storm/wind slabs. The slab may be 'upside down' with moist or wet snow blanketing the previous dry low-density snow. A surface hoar layer, buried at the start of January in the northern part of the region, may be around 40-60 cm deep now. In the mid-pack, a crust weakness buried in mid-December seems to have fallen off most operators' radar for now. Near the base of the snowpack is a November crust-facet combination that could remain problematic, especially in shallower snowpack areas with heavy loading and warming this week.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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.