The consequence of triggering a deep persistent slab avalanche warrants a cautious approach to steep open terrain.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY: Isolated flurries with up to 5 cm by the morning, light north winds, alpine temperatures around -8 C.TUESDAY: Cloudy with sunny periods, light northwest winds, alpine temperatures around -10 C.WEDNESDAY: Mix of sun and cloud, light northwest winds, alpine temperatures around -10 C.
Avalanche Summary
No new avalanches were reported on the weekend. Wind slabs are possible to trigger in isolated locations, but the main concern continues to be the possibility of triggering the weak faceted layers deeper in the snowpack.
Snowpack Summary
A dusting of new 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 with 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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.