*** UPDATE*** Heavy loading from snow and wind is likely resulting in large natural avalanches. Travel in avalanche terrain is not recommended without professional-level safety systems.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
FRIDAY: Cloudy with flurries bringing another 10-15 cm of fresh snow, moderate to strong southwesterly winds, and alpine temperature around -5 C with freezing levels below valley bottoms.SATURDAY: Cloudy with flurries bringing another 5-10 cm of fresh snow, moderate to strong southwesterly winds, with freezing levels around 1200 m.SUNDAY: A mix of sun and cloud with isolated light flurries possible, strong southwesterly winds and freezing levels as high as 1600 m.
Avalanche Summary
Reports from Wednesday include several relatively harmless thin storm slab avalanches. Reports from Tuesday include several explosives-triggered avalanches up to Size 2.5, one of which failed to ground in some lower moraine features. A Size 1.5 slab was triggered by a ski touring party in the central part of the region on Sunday. The slide initiated in a wind loaded pocket on a southwest aspect at 2100 metres and featured a 100cm deep crown fracture. While it is not believed to have involved persistent weak layers, it does reveal the scale of recent wind slab growth as well as their remaining sensitive to light triggers in specific terrain. Another relatively recent report includes details of a remotely triggered Size 2.5 avalanche that occurred in the south of the region on Thursday. The slide took place on a roughly 30 degree south-facing slope at 2100 m in elevation. The remote trigger, a depth of 80 cm, and a failure plane attributed to our January 15 surface hoar all reinforce enduring concerns for persistent slab problems in the region.
Snowpack Summary
Another 10 cm adds to 10 cm of recent snow that buried old wind slabs lurking on a variety of aspects in wind-exposed terrain. While these old wind slabs are suspected to be growing stubborn, the fresh snow is likely forming new touchy slabs in wind exposed areas. In more sheltered areas, the new snow has buried faceted surface snow as well as surface hoar existing on sheltered open slopes. The persistent weakness buried mid-January is now down 50-100 cm and consists of buried surface hoar in sheltered areas, and/or widespread faceted old snow. It has generally stabilized but may remain reactive in isolated areas where buried surface hoar is preserved. Another surface hoar/facet weakness buried mid-December can now be found down about 70 cm in shallow snowpack areas. While reactivity at this layer has declined, professionals in the region are still treating it with a great deal of caution.It should be noted that areas in the far south of the region saw as much as 25 cm of new snow over the course of the recent storm, coupled with strong winds. In these areas, the wind slab problem should be treated with considerably more caution.
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.