New snow amounts are expected to vary across the region. Bump up the treeline rating to HIGH if there's more than 25 cm new snow; bump the alpine rating down to Considerable if there's less than 15 cm.
Confidence
Fair - Intensity of incoming weather is uncertain on Thursday
Weather Forecast
20-30 cm new snow overlies a crust that exists on south aspects to around 1900 m and on other aspects to around 1700 m. Recent winds have blown the new snow into wind slabs in exposed lee terrain. Below the crust, two persistent weak layers from mid-February are still being tracked by professionals. The upper one, buried around 16th Feb, is buried approximately 150 cm. The lower one, buried around 9th Feb, is buried typically 180 cm in high snow areas, but as little as 90 cm in low snow areas. Snowpack tests indicate, while both surface hoar layers are becoming more difficult to trigger, they still have the potential to release avalanches, with regular sudden, 'pop' results still being observed.
Avalanche Summary
On Tuesday, wind slabs in the size 1-1.5 range were triggered naturally and by skiers at treeline and above on slopes loaded by south-westerly winds. On Sunday, a size 1.5 avalanche released naturally on a north aspect. On Saturday, a recent avalanche was observed on a north aspect in the southern Elk Valley, suspected to have started as a wind slab and ending in moist snow. Evidence of a previous natural cycle was also reported. On Friday, explosives produced size 1-2 avalanches.
Snowpack Summary
20-30 cm new snow overlies a crust that exists on south aspects to around 1900 m and on other aspects to around 1700 m. Recent winds have blown the new snow into wind slabs in exposed lee terrain. Below the crust, two persistent weak layers from mid-February are still being tracked by professionals. The upper one, buried around 16th Feb, is buried approximately 150 cm. The lower one, buried around 9th Feb, is buried typically 180 cm in high snow areas, but as little as 90 cm in low snow areas. Snowpack tests indicate, while both surface hoar layers are becoming more difficult to trigger, they still have the potential to release avalanches, with regular sudden, 'pop' results still being observed. If avalanches do release on this layer, they will go big. The most likely triggering mechanisms are a person traveling over a thin snowpack area, or a storm slab, wind slab or cornice stepping down. Basal facets may still exist, particularly in shallow snowpack areas with steep, rocky start zones. Cornices have grown large and threaten slopes below.
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.
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.
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.