Regions
Northwest Inland.
Winds are driving slab problems at higher elevations. Chances of triggering a storm slab or even a deeper persistent slab are increased at lower elevations.
Weather Forecast
Saturday night: Flurries bringing approximately 5 cm of new snow. Moderate to strong southeast winds. Sunday: Cloudy with continuing scattered flurries bringing 2-5 cm of new snow. Moderate southeast winds. Alpine high temperatures around -7.Monday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Alpine high temperatures of -7.Tuesday: Mainly cloudy with flurries beginning in the afternoon. Moderate to strong southeast winds. Alpine high temperatures of -8.
Avalanche Summary
Reports from Friday show 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 (from a distance) triggers on the mid-December weak layer, found 50 cm below the surface. Reports from Thursday included one observation of numerous natural storm slab releases from Size 1-2 north of Kispiox. These were noted running on relatively low angle terrain and suspected to have released over a layer of surface hoar that may not be widely distributed. Another few Size 2 natural storm slab releases were noted in very steep north aspects around treeline elevations in the Howsons.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
Snowfall from last week brought a variable 10-20 cm of new snow to the region. The new snow has buried a temperature crust that likely 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. This surface hoar is noted in our avalanche activity discussion for having produced numerous storm slab releases in a localized area after the storm ended. 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.