It may continue to be possible to trigger a deep persistent slab avalanche in shallow snowpack areas.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Cloudy with light northwest winds overnight and alpine temperatures -10. Broken skies on Wednesday with light westerly winds and freezing at valley bottoms. Mostly sunny on Thursday with light southwest winds and alpine temperatures around -5. Mix of sun and cloud on Friday with light winds and alpine temperatures -5.
Avalanche Summary
Small size 1 loose dry avalanches have been reported in steep terrain. The main concern continues to be the possibility of triggering the weak faceted layers deeper in the snowpack.
Snowpack Summary
Up to 10 cm of low density snow sits above hard wind-affected surfaces, while a recent melt-freeze cycle has left a hard crust at lower elevations (up to 1400 m in the west and 1900 m in the east). The snowpack is quite variable throughout the region. In deeper snowpack areas, the snowpack appears to be well settled with isolated concerns about the mid-December facet layer buried 50-100 cm deep. In shallow snowpack areas and lower elevations, the snowpack is weak and faceted. In these areas, winds have formed isolated hard slabs above weak facets and created the potential for large persistent slab avalanches.
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.