A Special Public Avalanche Warning Applies for this Region.Heavy loading from snow and wind is expected to result in natural avalanches, especially in the southern parts of the region.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
THURSDAY: Mainly cloudy with 15-25 cm of fresh snow, moderate to strong southwesterly winds, and freezing level remaining near valley bottoms.FRIDAY: Cloudy with scattered flurries bringing approximately 5 cm of fresh snow, moderate to strong southwesterly winds, and freezing level remaining at valley bottoms.SATURDAY: A mix of sun and cloud with isolated light flurries possible, moderate westerly winds, and freezing levels below valley bottoms.
Avalanche Summary
Reports from Tuesday include numerous explosives-triggered storm slab avalanches up to Size 2.5, with one Size 1 ski cut. Further evidence of numerous recent natural storm slab avalanches up to Size 2 was also reported. Also, a skier accidentally triggered a 50cm thick Size 2 storm slab avalanche on a southwest aspect at 2200 m.Heavy loading from snow and wind is expected to result in continued natural avalanche activity.
Snowpack Summary
Fresh snow totals from the past few days are around 50-100 cm in the southern part of the region, with the northernmost tip of the region only receiving about 25 cm of new snow. This recent storm snow has settled into a slab, especially where it has been wind-loaded, which is bonding poorly to the previous snow surface that includes sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. Weaknesses are also lingering within the recent storm snow, with 'upside-down' conditions and several easy to moderate shears being reported. A persistent weakness buried mid January is now down 60-120 cm and consists of buried surface hoar in sheltered areas, sun crust on south aspects, and/or faceted old snow. It has generally stabilized but may be sensitive to triggering in isolated areas where surface hoar is preserved. Another surface hoar/facet weakness buried mid-December found 70-140 cm is generally considered dormant. This and deeper persistent weaknesses remain concerns isolated to shallow snowpack areas where they lie closer to the surface.
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.