Several deeply buried weak layers are a major concern in this region and warrant conservative terrain choices. Stick to simple low-angle terrain and avoid overhead hazards like cornices.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
THURSDAY: Cloudy with isolated flurries / moderate west wind / alpine temperatures around -10 C.FRIDAY: Isolated flurries / moderate to strong west wind / alpine temperatures around -7 C.SATURDAY: Moderate snowfall (amounts uncertain at this point) / strong northwest winds / alpine temperatures around -3 C.
Avalanche Summary
On Wednesday, a few natural wind slabs (size 2) were reported north of Elkford, including some triggered by cornices. A large deep persistent slab with wide propagation was also reported in alpine terrain. On Tuesday, a few natural wind slabs (size 2) were reported in the southeast part of the region.During the warm stormy weather on Sunday and Monday a few large deep persistent slab avalanches were reported (up to size 3), most of which were triggered by cornices on north and east facing slopes. Most large slab avalanches have failed on the deeper November and December weak layers.
Snowpack Summary
The most recent snowfall was accompanied with strong gusty winds, leaving touchy slabs in the alpine and large fragile cornices. Warm temperatures on Monday left moist snow and crusts up to about 1700 m.About 20-50 cm of recent snow covers a weak layer that was buried in mid-January. It is composed of feathery surface hoar in sheltered areas and a sun crust on solar aspects. Another surface hoar layer from early-January is buried 30-60 cm deep. A widespread weak layer from mid-December is composed of facets, crusts, and surface hoar and is now buried 60-80 cm deep. Finally, a weak layer of rain crusts and sugary facets buried in late-November exists near the base of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread. Snowpack depths are also variable across the region and typically thinner in northern areas than in areas to the south.
Problems
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.
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.