Watch for reactive storm slabs to form as the new snow settles. Tricky conditions still exist due to a touchy weak layer. Conservative terrain selection is critical.
Confidence
Moderate - Freezing levels are uncertain on Monday
Weather Forecast
SATURDAY: Up to 15cm snow overnight, with another 5cm possible thought he day, rain is expected at lower elevations, moderate to strong westerly winds, freezing level of 1500m overnight falling to 1000m in the day. SUNDAY: Mainly cloudy, light westerly winds, freezing level falling to valley floor though the day. MONDAY: sunny with cloudy periods, light westerly winds, freezing level around 2500-3000m, +5C at 2500m.
Avalanche Summary
The recent storm snow is becoming increasingly reactive with numerous small natural and human triggered avalanches reported in the last two days. The January surface hoar remains a concern. A size 3 natural avalanche that occurred earlier in the week at treeline near Blue River was reported to be around 1500m wide, demonstrating the ability of this layer to propagate and produce large destructive avalanches. On Sunday, a helicopter is believed to have remotely triggered a size 2.5 persistent slab avalanche at the 1900m elevation from a distance of 200m. This slab was about 400m wide, 90cm deep and is thought to have failed on the early January surface hoar. Although both of these avalanches occurred on the east side of Highway 5 (technically in the Northern Monashees), similar touchy conditions likely exist in many parts of the Cariboos.
Snowpack Summary
Up to 45cm of recent storm snow is settling to form a widespread soft slab. Moderate southwesterly winds have formed fresh wind slabs in lee features at treeline and in the alpine. Below 1800m this new snow is sitting on a crust. Several touchy layers of surface hoar from early to mid-January are now buried between 70 and 120cm deep and are variably reactive. In other words, some slopes are difficult to trigger while remote triggering is still possible on other features. These layers have the potential for wide propagations, and smaller avalanches could step-down to one of these layers. Snowpack depths are variable across the region and shallow snowpack areas may have weak facetted crystals near the ground.
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.