Regions
Northwest Inland.
The Avalanche Danger may be slightly higher in the far southwest of the region where recent snowfall amounts were the greatest.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
An active weather pattern will deliver continued precipitation to the region for the forecast period. Expect daily accumulations of 3-8cm with freezing levels hovering around 800m. Ridgetop winds will be strong to extreme from the southwest on Monday, decreasing to moderate from the south on Tuesday and Wednesday.
Avalanche Summary
Last week, a size 3 deep persistent slab avalanche was accidentally triggered by a skier in alpine terrain in the north of the region. The slab, which ran on basal facets, was up to 200cm deep, 200m wide and 500m long. There have been a handful of recent similar avalanches triggered on basal facets in the mountains north of Kispiox. On Friday, a widespread round of storm slab activity to size 2 was reported from the southwest corner of the region where recent storm accumulations were the greatest. Of note, a size 3 natural storm slab avalanche was also reported from the Howson Range area on a steep, north-facing alpine slope. Ongoing wind slab activity is expected in response to continued snowfall and extreme winds.
Snowpack Summary
Over the past few days daily snowfall accumulations have generally been in the 5-15cm range with the highest accumulations occurring in the southwest of the region. Strong to extreme ridgetop winds have shifted the new snow into new wind slabs at treeline and in the alpine adding to an ongoing wind slab problem. A layer of surface hoar from early January can be found in isolated locations between 60 and 140cm down. There hasn't been any activity reported on this layer for a couple of weeks now and it is becoming less of a concern. In shallower areas the snowpack sits on a weak base layer of facetted snow. Recently, this layer has been active in the north of the region, responsible for several large avalanches in unsupported alpine terrain.
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.