The February 12th persistent weak layer continues to be a concern across the Interior Regions. Avalanches failing on this layer of buried surface hoar will be large and destructive.
Confidence
Fair - Timing or intensity of solar radiation is uncertain for the entire period
Weather Forecast
Overnight and Thursday: High cloud with light Northwest winds combined with light precipitation as a weak low pressure system tracks along the U.S. border. Freezing level rising to about 1100 metres.Friday: The ridge is expected to continue to influence most of the province bringing high overcast cloud to the South of the region and a trace of snow at higher elevations. Freezing level rising to 1300 metres.Saturday: Mostly cloudy with a chance of light precipitation in the afternoon.
Avalanche Summary
Some loose snow sluffing up to size 1.0 and a couple of size 2.0 wind slab releases were reported from Tuesday. There were also a couple of natural cornice falls to size 2.0 that did not release down to the deeply buried weak layers.
Snowpack Summary
A light dusting of new snow is sitting above various sun crusts and old storm slabs. The storm slab continues to settle, and is becoming more stubborn to trigger. The weak layer of surface hoar that was buried on February 12th is now down about 100-150 cms and continues to be triggered by light additional loads on Southerly aspects where it is sitting on an old sun crust. Larger loads like cornice fall or explosives have been able to trigger this layer on various aspects in the alpine and at treeline. If the we get a period of strong solar radiation, then we may see another cycle of natural activity on Southerly aspects resulting in large destructive avalanches.
Problems
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.
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.