Regions
Northwest Inland.
A complex snowpack has begun to take shape in the Northwest. Choose terrain that is unlikely to release a storm slab and you'll likely avoid triggering the more dangerous persistent slab lurking beneath it.
Confidence
Low - Due to the number of field observations
Weather Forecast
Friday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Moderate to strong southwest winds. Alpine temperatures around -5.Saturday: Mainly cloudy with scattered flurries and a approximately 5 cm of new snow. Moderate south winds. Alpine temperatures around -4.Sunday: Cloudy with isolated flurries and a trace to 5 cm of new snow. Moderate south winds. Alpine temperatures of -3.
Avalanche Summary
One report from Wednesday discussed several estimated Size 2.5-3 avalanches observed on the Kathlyn face of Hudson Bay Mountain. No other new avalanches have been reported, which almost certainly owes more to a lack of observers than a lack of avalanche activity and potential. Please post your observations to the Mountain Information Network. (MIN)
Snowpack Summary
Snowpack depths over the region are above average for late November, with approximately 150 cm of settled snow present at treeline elevations and above. Stormy weather over the mid-week delivered about 30 cm of new snow to the region, forming storm slabs which are expected to be particularly reactive in open terrain where wind effects promote more variable loading. Mid-treeline and lower elevations did receive some precipitation as rain toward the end of the storm, but his thin rain layer is not expected to offer much bridging strength to the snowpack. About 20-30 cm of recent storm snow lies below this week's accumulations and above the widespread late October crust. The October crust is present near the base of the snowpack at all elevations and features a layer of weak, sugary grains above it. This "crust/facet combo" layer remains an ongoing concern for step-down potential from large triggers such as a storm slab release. The crust is less of a concern below treeline where it is broken up by vegetation near the ground.
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.
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.