Regions
Northwest Coastal.
Sun and solar radiation may have a significant destabilizing effect on the snowpack. As freezing levels rise throughout Saturday, so will the Avalanche Danger.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Friday's storm system will dissipate on Saturday as a weak ridge develops. On Sunday and Monday, the ridge will flatten-out allowing for a series of pacific system to impact the region. Saturday: Generally clear skies with valley fog / Light northwest winds / Freezing level at 1600m Sunday: Up to 15cm of new snow / Moderate southwest winds / Freezing level at 400m Overnight Sunday and Monday: Up to 25cm of new snow / Moderate southwest winds / Freezing level at valley bottom
Avalanche Summary
At the time of publishing this bulletin, there was no new avalanche activity reported from the field. That said, I'm sure there was a healthy round of storm slab activity in response to heavy snow accumulations on Friday. Looking forward, I'd remain cautious of recently formed storm slabs, as they may remain sensitive to human triggering, especially in wind-exposed terrain. Additionally, persistent weak layers should remain on your radar as they may become reactive with the loading of the new snow, or with warming and solar radiation forecast for Saturday. Any avalanche on these deeper persistent weaknesses would be destructive in nature.
Snowpack Summary
Moderate to heavy snowfall (with rain at lower elevations) and strong southwest winds have likely built deep and dense storm slabs. These storm slabs are expected to be most reactive in wind-exposed, upper elevation terrain. A rain crust and/or surface hoar layer buried mid-January can be found about 100cm below the surface, the depth varying greatly depending on whether the slope is wind-loaded or wind-scoured. The structure of this layer may have strengthened somewhat. Still, I would recommend giving this layer a little more time to bond before discounting it from the avalanche equation. The November crust/ facet combo near the bottom of the snowpack is thought to be generally well bonded. However, this deep and destructive layer is still reported to be reactive in the far north of the region.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.