A storm is incoming, but total snowfall amounts for Thursday night into Friday are uncertain. The forecast herein assumes 30+ cm of snow accumulation by Friday afternoon.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
THURSDAY NIGHT: Cloudy with snowfall, accumulation 15 to 30 cm, alpine temperature -10 C.FRIDAY: Cloudy with snowfall, accumulation 5 to 15 cm, moderate to strong southwest wind, alpine temperature -8 C.SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, light to moderate southwest wind, alpine temperature -13 C.SUNDAY: Mostly cloudy with light snowfall, accumulation 5 cm, light north wind, alpine temperature -20 C.
Avalanche Summary
There was a natural avalanche cycle that occurred on Wednesday, with many large (size 2 to 3) storm slab avalanches observed. The avalanches were generally 20 to 40 cm deep, on northerly aspects, and within all elevation bands.
Snowpack Summary
More snowfall is expected Thursday night into Friday, with total amounts uncertain but could be upwards of 20 cm or more. This new snow will overly around 30 to 50 cm of recent snow, which sits on variable layers, including wind-affected snow at treeline and alpine elevations, feathery surface hoar crystals in shaded and sheltered areas below treeline, and a melt-freeze crust below 1600 m.The mid-January layer of surface hoar or a crust is buried around 70 cm. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m. The melt-freeze crust is found on south aspects at all elevations.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may find weak and sugary faceted grains near the base of the snowpack.
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.