Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
The arrival of the next frontal system should come Monday night into Tuesday bringing light-moderate snowfall amounts which will intensify later Tuesday into Tuesday night.Tuesday: New snow up to 15cm. Ridgetop winds 40-50km/hr from the West. Treeline temperatures near -3, with freezing levels up to 1500m. Wedneday: Snow amounts 5-10cms. Ridgetop winds from the West reaching 70-90km/hr, slowly dying to 40-60km/hr in the afternoon. Freezing levels falling to 1000m. Thursday: Trace amounts. Ridgetop winds from the NW 50-70km/hr.
Avalanche Summary
Coquilhalla Area: Skier triggered size 1 was reported. This occurred on an East aspect, @ 1845m. The crown was 20cm deep, and 10m wide. Another skier triggered avalanche size 1.5 occurred on a North aspect @ 1460m. This was below treeline in a gully feature. Both avalanches failed on the buried weak layer that exists below the new storm snow. No injuries reported.Duffy Lake area: On Saturday a size 2 rider triggered avalanche was reported, to see more details visit our incident report database: https://avalanche.ca/cac/library/incident-report-database/view/ffa0801e-2d0e-48e8-b480-5b6068d5a8bb
Snowpack Summary
Over the weekend up to 20cm of new snow fell over the Duffy Lake area. The Coquihalla has seen up to 40cm. This new snow has buried a variety of old snow surfaces that formed during a sunny dry spell over the past 2 weeks. These surfaces include: melt-freeze crusts on all aspects below 1700m and on steep solar aspects higher up, surface hoar (feather like crystals), old wind slabs, and facets (sugary crystals), which exist on north aspects as well as around crusts. The surface hoar seems to be most prominent in sheltered treeline locations and below, and most likely found in the north and central parts of the region. We may see these buried weak layers become naturally reactive with forecast snow and wind, and likely susceptible to rider triggers. Generally below this sits a well settled snowpack, with treeline snowpack depths near 250cm. For insight on incremental loading, and the "Tipping Point" check out our latest Forecaster's Blog.
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.