Regions
Northwest Coastal.
Confidence
Fair - Intensity of incoming weather is uncertain for the entire period
Weather Forecast
Wednesday: Snow with 10-15cm of accumulation throughout the day, freezing levels rising throughout the day to near 800m for coastal areas, and moderate southwesterly winds increasing to strong southerlies by the afternoon. Thursday: Continued snowfall overnight with an additional 10-15cm by Thursday morning with an additional 15-20cm throughout the day accompanied by strong southerly winds. Freezing levels rising as high as 1000m by the evening. Friday: A warm and very wet system is expected to blow over Thursday night with an additional 20-25cm by Friday morning when it is currently expected to dry out throughout the day. Freezing levels are expected to peak at 1000m and gradually lower as things dry out. Strong to extreme southerly winds associated with the height of the storm should also diminish and shift to southwesterlies as things dry out throughout the day on Friday.
Avalanche Summary
Recent reports include observations numerous natural loose-snow avalanches up to Size 2 on all aspects at all elevations from the weekend. These avalanches were generally dry in alpine areas and on shaded slopes, and moist below treeline and on sun-exposed slopes at treeline. Several natural slab avalanches up to Size 2 were also observed on southeast through west aspects in the alpine. On Monday 20cm deep Size 1.5 soft wind slab avalanche was skier-controlled on a northwest facing alpine feature, but extensive slope cutting on large steep alpine slopes and a couple of very large controlled cornice drops didn't trigger any avalanches. A very large natural ice fall avalanche also occurred on a glacier in Bear Pass.
Snowpack Summary
New snow is adding to the recent settled storm snow overlying a crust, old wind slab, and/or surface hoar depending on location, aspect and elevation. Last week a snowpack test in the Shames Valley resulted in a sudden planar shear on the buried surface hoar, down around 60 cm at the time. Most areas are reporting that the snow has bonded well to the underlying crust. The mid and lower snowpack is generally well settled and strong. The exception seems to be shallow snowpack areas where basal facets are are a concern.
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.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.