High freezing levels with rain and strong winds mean that the snow pack may take time to stabilize. Conservative decision making is still recommended.
Confidence
Poor - Due to the number and quality of field observations
Weather Forecast
A second warm wet weather system will hit the coast on Sunday although a week ridge of high pressure will protect the interior from the brunt of this system and I expect the region will see only light flurries or showers on Sunday. Warm temperatures and moderate to strong SW winds will persist through until Tuesday
Avalanche Summary
Recent snow, forecast rain, warm temperatures and high winds are a recipe for an avalanche cycle, especially when you throw in a couple of prominent weak layers. I anticipate an active cycle to continue on Sunday. Previous avalanche activity during and after the last storm system was widespread, with avalanches releasing up to size 3.5 on a variety of aspects and elevations.
Snowpack Summary
Between 20 and 30 cm of new snow (and possibly rain at lower elevations) fell in the last storm which I suspect is rapidly settling into a soft slab. This new snow sits upon a moderately dense upper snowpack. A weak layer of surface hoar lies buried between 60 and 90 cm below the surface, and may sit above a crust, particularly on south-facing slopes. This "mid-January" weak layer is widespread and has been the main focus for recent avalanche activity. I suspect that it will continue to produce avalanches through the weekend as the snow pack adjusts to the recent snowfall and continued warm temperatures. The still problematic mid-December surface hoar/crust layer is now typically 90-160cm below the surface. While snowpack tests indicate this layer is gaining strength in many areas, avalanches were still noted on this layer from the last storm cycle, which suggests we still need to it into our decision making process. It has been most reactive in the 1600-1900 m elevation band.
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.
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.