Regions
Northwest Coastal.
I've kept the Avalanche Danger at HIGH for one more day. With the benign weather pattern, the chances of triggering a slide will decrease, but the consequences could be disastrous. Conservative terrain selection remains critical.
Weather Forecast
On Saturday and Sunday expect generally overcast skies and isolated flurries. Freezing levels for the weekend should hover around 450m while ridgetop winds should be mainly light from the north. On Monday, the region may see 3-5cm of new snow. Winds on Monday may increase to moderate from the southwest while freezing levels should drop to valley bottom.
Avalanche Summary
In recent days observations have limited due to stormy weather; however, professional operators in the region were still reporting fairly widespread explosive and naturally triggered large storm and persistent slab avalanches to size 3.5. Many of these avalanches are thought to have failed on the January 9th surface hoar. Forecast cooling and should help gradually reduce natural avalanche activity. But, for the short term storm slabs will likely remain sensitive to light loads, while potential remains for very large and highly destructive persistent slab avalanche activity.
Snowpack Summary
A warm, wet and windy storm has formed deep, dense and reactive storm slabs at higher elevations while rain has saturated the snowpack on many slopes below treeline. The snow line fluctuated a great deal during the storm which dropped around 80mm of precipitation in the Terrace area (and slightly less in the mountains around Stewart) over the past 5 days. The January 9th surface hoar/facet layer is down 70-150 cm in most places, and is a concern on all aspects and elevations. Around the same depth you may also find a surface hoar/facet interface from around New Years. The hope is the combination of heavy storm loading and warm temperatures has flushed out these weak layers in many areas, but professionals have noted the snowpack did not see extensive rain at critical elevations. In short, the buried surface hoar is still an issue. In the wake of the storm, there will be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem. Additionally, the snowpack will require time to adjust to the stress of heavy storm loading. A very conservative approach to mountain travel is still required.
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.