Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
An approaching low pressure system will bring moderate-heavy precipitation to the coastal regions beginning Thursday night into Saturday. Friday: Snow amounts 15-25 cm. Ridgetop winds 30km/hr from the SE. Treeline temperatures near -5. Freezing levels 500m. Saturday: Snow ending by midday with scattered flurries. Ridgetop winds light -moderate from the SW. Freezing levels at valley bottom. Sunday: Light flurries during the day. Ridgetop winds light from the NW. Freezing levels valley bottom.
Avalanche Summary
Coquilhalla Area: Several natural size 2-2.5 slab avalanches occurred on West aspects. Crown depths being 50-100cm, and running 100m in distance. Skier triggered size 1.5 failed on the above mentioned graupel layer, @1650m on an East aspect, running 100m in length.
Snowpack Summary
Over the past week 20-30 cm of new snow fell over the Duffy Lake area, this snow fell incrementally and low density. The Coquihalla has seen up to 50 cm. This new snow has buried a variety of old snow surfaces. The old 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. I suspect these buried weak layers will become naturally reactive with forecast snow and wind, and the slopes that don't slide naturally may be ripe, waiting for a rider trigger. Below this sits a well settled snowpack, with treeline snowpack depths near 250cm. Test results on the Duffy today shows RB4 down 35cm on 3mm Surface Hoar, sudden planar results. The warning signs are clear and a large avalanche cycle has started in the interior regions. Please visit our Forecaster's Blog for more detailed information. To view recent photos of this buried surface hoar in the Coquihalla area please check out this link:https://avalanche.ca/cac/library/avalanche-image-galleries/avalanches2012
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.