Regions
Northwest Coastal.
Forecast new snow and wind will increase the avalanche danger. Buried surface hoar may allow for long fracture propagations resulting in larger avalanches.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Thursday
Weather Forecast
Southerly winds are forecast to push cloud into the region this evening. Snow starting overnight with freezing down to valley bottoms. Expect 5-10 cm by Thursday morning and another 5-10 during the day combined with strong southerly winds. Heavier snowfall amounts are possible west of Terrace and in the south near Kitimat. Overcast with freezing down to valley bottoms on Friday with light snow during the day becoming moderate snow in the evening. Expect 10-20 cm by Saturday morning with snow and strong winds continuing during the day.
Avalanche Summary
No new avalanches reported. I suspect that pockets of wind slab may continue to be triggered by light additional loads in the alpine and at treeline. New storm slabs are expected to develop with the incoming storm.
Snowpack Summary
Outflow winds were limited on Wednesday to below 400 metres and did not transport much snow or destroy new surface hoar. The surface hoar layers are getting difficult to track by name, so lets talk about them by burial date. There is a new surface hoar layer developing now that has not been buried yet, but that should happen tonight. The forecast new snow and wind are expected to add to the load above the December 14th surface hoar (151214 SH) which was reported to give easy compression test results today with a sudden planar fracture character (CTE SP). This means that as a slab develops above this layer, it may allow for long fracture propagations resulting in larger avalanches. At this time there is 15-25 cm above the 151214 layer in the Shames area. The early December layer buried on the 1st or 2nd (151201 SH) is now down a metre or so depending on your area. This layers distribution is variable. In some areas, this layer may be sensitive to human triggering and wide propagations while in other areas it is non-existent or has gained significant strength.
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.