Click on the 'Forecaster's Blog' link below for more discussion on how to safely approach backcountry travel under the current conditions.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Sunday: Light to moderate snowfall through the day, with the freezing level near 1000m. Strong south-westerly winds at ridgetop. Storm snow totals should reach around 15cm on average by Sunday, with local variations. Expect enhanced amounts on the western side of the range.Monday: Moderate precipitation at times, with the freezing level slowly rising to 1200m. Moderate-strong south-westerly winds.Tuesday: Confidence for Tuesday's weather is limited, but we're currently expecting moderate snowfall at times, with a rising freezing level.
Avalanche Summary
No new avalanches have been reported since Wednesday. It's a big area, however, and we receive limited reports. Earlier in the week, a natural avalanche cycle was observed in the South Cariboos, mostly on north aspects in the alpine. Several rider-triggered avalanches occurred, with the mid-December hoar/facet/crust interface causing most concern. With new storm slabs and wind-slabs building over these known weaknesses, further avalanche activity remains a distinct possibility.
Snowpack Summary
Recent storm snow continues to be redistributed by southwest winds. Wind slabs with the potential to propagate widely exist in the alpine, particularly on north through east aspects. At treeline and below, pockets of wind slab also exist in open areas. A surface hoar/facet/crust interface is buried anywhere from 30- 80cm deep and has recently proven itself to be variable in its distribution, with concerning (sudden planar) results in snowpack tests and rider-triggered avalanches in some places and little results in other places. This means the problem is somewhat spotty, but could be lurking round the corner - and have huge consequences if triggered.A resistant-type shear about 30cm down within the recent storm snow also exists. A sun crust also exists in the alpine on steep south and west aspects. The mid-pack is generally strong and well settled.
Problems
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.
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.