Regions
Northwest Inland.
Expect change to be slow. Wind slabs will be slow to bond, and deep persistent weak layers will continue to be a concern for large avalanches.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Some thin high cloud overnight with strong northeast winds. Cold and clear on Tuesday with temperatures 5-10 degrees warmer in the alpine than in the valleys. Cold and clear on Wednesday with light-moderate northerly winds, some chance of a weak above freezing layer in the alpine. Cloud developing on Thursday with moderate westerly winds and no new precipitation.
Avalanche Summary
In the north of the region near Ningunsaw there was a natural avalanche size 3.5 that released in the basal facets on Monday. This is a good reminder that large full depth avalanches are possible in shallow snowpack areas. A natural avalanche cycle with slides up to size 2 occurred Friday in the mountains near Smithers. This was in response to the strong northerly winds. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds redistribute any loose surface snow. Deeper persistent weak layers will also remain a concern, it is possible to trigger large avalanches.
Snowpack Summary
Snowpack depths in this region are still shallow - around 1 m or so, meaning there are a lot of weak sugary facets in the snowpack. Recent storm snow is being redistributed by strong to extreme winds, and wind slabs are widespread behind exposed features. Where hard wind slabs overlie weak facets, the structure is ripe for human-triggered avalanches.In addition to the sugary facets, you may find a layer of feathery surface hoar (up to 15 mm in sheltered areas), buried around 20 - 30 cm below the surface. There is another weak layer that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be found close to the bottom of the snowpack nestled in amongst the facets. We don't have a lot of information about these layers, but it's worth noting the layer responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.