Regions
Northwest Inland.
Increasing winds will be driving slab formation at higher elevations on Tuesday. At sheltered elevations where surface hoar exists, storm snow is gradually settling into an overlying slab even without the effect of the wind.
Weather Forecast
Tuesday: Cloudy with scattered flurries bringing 2-5 cm of new snow, increasing overnight. Moderate to strong southeast winds. Alpine high temperatures of -9.Wednesday: Mainly cloudy with continuing isolated flurries and a trace of new snow, continuing overnight. Light to moderate southeast winds. Alpine high temperatures of -6.Thursday: Cloudy with continuing scattered flurries bringing 2-5 cm of new snow. Light southeast winds. Alpine high temperatures of -10.
Avalanche Summary
Reports from Saturday included one remotely (from a distance) triggered Size 1.5 wind slab releasing from a steeper northwest-facing slope at around 1500 metres. The slab depth was 40-60 cm.Friday's reports showed a notable increase in persistent slab activity at lower elevations in the Howson Range. In this area, three Size 2 releases failed on steeper terrain with remote triggers on the mid-December weak layer, found 50 cm below the surface. Another report from last week mentioned numerous natural storm slab releases from Size 1-2 north of Kispiox. These were suspected to have released over a layer of surface hoar that may not be widely distributed.Looking forward, our storm slab problem is diverging into more distinct wind slab problems at higher elevations and more isolated storm slab over surface hoar issues at mid elevations. Lower elevations have become an increasing concern in areas where the upper 50 cm of the snowpack has settled into a slab over the persistent mid-December weak layer.
Snowpack Summary
Recent light snowfalls have gradually brought about 20-30 cm of new snow to the region. The new snow has buried a temperature crust that exists well into the alpine. There are also reports of more isolated pockets of surface hoar beneath the new snow at lower alpine and treeline elevations. While its distribution is uncertain, this surface hoar remains an ongoing concern as the overlying storm snow settles into a slab above it.Below the new snow interface, deeper weak layers in the snowpack include a few crusts and surface hoar layers that formed in early January and December. Most recent reports suggest the snow is well bonded to these layers, but recent persistent slab activity over a surface hoar and facet 'combo' at low elevations suggests that a dangerous persistent slab problem may be developing as the mid and upper snowpack consolidate into a stiffer slab over this layer.
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.