Regions
Northwest Coastal.
Continued wind, snow and warming will add more stress to buried weak crystals. Very large avalanches have been running from the alpine to valley bottom. Conservative terrain selection remains critical.
Confidence
Fair - Track of incoming weather systems is uncertain on Monday
Weather Forecast
An active moisture stream will continue to bring moderate snowfall with locally heavy accumulations in the south of the region. Monday night: Up to 30cm of new snow / Extreme southwest winds / Freezing level at 1200m Tuesday: Moderate snowfall in the morning easing by mid-day / Strong southwest winds / Freezing levels at 800m Wednesday: Light snowfall with up to 15cm falling that evening / Strong southwest winds / Freezing level at 800m Thursday: About 10cm of new snow / Extreme southwest winds / Freezing level at 1200m
Avalanche Summary
In recent days, a widespread natural avalanche cycle took place to size 3.5. These avalanches were triggered by loading from heavy precipitation, wind, and warm temperatures. Many avalanches failed within the recent storm snow, although numerous avalanches also failed on persistent and deep persistent layers. At lower elevations where precipitation fell as rain, loose wet avalanches to size 2 were also observed. With ongoing loading from new snow and wind, I expect ongoing storm slab activity with the potential for deeper destructive releases.
Snowpack Summary
Ongoing heavy snowfall (with rain below approximately 1200 m) and extreme southwest winds continue to build fresh deep and dense storm slabs. A rain crust and/or surface hoar layer buried mid-January is buried about 100cm below the surface. This weakness became reactive with recent heavy loading, and has been responsible for much of the recent large avalanche activity. The November crust near the bottom of the snowpack is generally well bonded, but has woken-up in some cases with intense loading and warm temperatures throughout the past week. There is still potential for very large and deep avalanches.
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.
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.