Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Tonight and Thursday: The South Coast will remain under a ridge of high pressure bringing dry and warm conditions. Freezing levels are expected to reach 3200 m by tomorrow afternoon, moderate NW winds and mainly clear skies. Friday: The whole Coast is under the high pressure system, clear skies, moderate W winds and freezing levels reaching record levels of 3300 m. Saturday: A frontal system is expected to reach the coast, expect cloudier skies, mild temperatures and winds tapering down.
Avalanche Summary
Explosive control in the North Cascades produced a couple size 2.5 on N and NE aspects.In the same area, there was also some loose wet avalanches below treeline up to size 1. In the Northern part of the region, there was also report of remotely triggering a couple size 2 avalanches which would have run on basal facets in the alpine on NE aspects.
Snowpack Summary
The main concern is the unusual warming and solar radiation shock that the snowpack will take. This will weaken the snow and most likely increase natural avalanche activity on SE and S aspects, but also in shaded areas because of temperatures rising to plus 10 C in the alpine! As well as surface wet slabs and loose snow avalanches, there is the possibility of it stepping down to a deeper persistent weak layer (PWL) especially in the Northern part of the region. Recent obvious clues include recent natural avalanches, skier remote avalanches, whumphing and cracking and sudden planar tests results all associated with one or the other PWLs. The basal facet layer is found mostly in the alp. and at treeline in shallower snowpack areas. The late Nov. facet/crust layer is also found in these elevation bands and the newly buried surface hoar seems to be starting to heal with the recent mild temperatures. In the southern part of the region, where the early season snowpack was deeper, these persistent weak layers do not seem to be as prevalent. However, temperatures and solar radiation will be even stronger in this part of the region, making wet slabs and loose avalanches even more probable.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.