Tricky conditions exist due a complex snowpack and a touchy weak layer. Conservative terrain selection is critical.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
THURSDAY: cloudy with sunny periods and lingering flurries, light southerly winds, -8 at 1500m. FRIDAY: cloudy, moderate southerly winds, freezing level rising to 1700m. SATURDAY: snow starting overnight with 5-7cm by morning, flurries continuing through the day, light to moderate westerlies, freezing levels falling to 1500m.
Avalanche Summary
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. The slab was about 400m wide, 90cm deep and is thought to have failed on the early January surface hoar. Although this avalanche occurred on the east side of Highway 5 (technically in the Northern Monashees), similar touchy conditions likely exist in many parts of the Cariboos. With that, a few size 1 naturally triggered persistent slab avalanches were also noted in the Cariboos on Monday on a northeast aspect at 1600m. The early January surface hoar was the culprit in both of these slides.
Snowpack Summary
Between 30 and 50cm of snow has fallen recently and remains mostly unaffected by wind. Isolated pockets of wind slab may be found in the immediate lee of ridge crest that may remain sensitive to light loads. Bellow 1500m this new snow is sitting on a supportive crust. Several touchy layers of surface hoar from early to mid-January are now typically down 70-120cm 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 have the potential to 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
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.