Regions
Northwest Coastal.
Extreme warming and solar radiation will drive the Avalanche Danger. Be alert to conditions that change throughout the day, and watch your overhead hazard. Very large avalanches may reach their run-out zones.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
A dry ridge of high pressure will bring mainly clear skies for Thursday and Friday. Increased cloud and isolated flurries are forecast for Friday evening and Saturday. The freezing level will spike to about 2800m on Thursday and then hover around 2400m on Friday and Saturday. Ridgetop winds will remain mainly light and variable.
Avalanche Summary
Stormy weather has limited avalanche observations, although I'm sure there was a decent round of natural storm slab activity in response to new snow and wind on Tuesday. As temperatures rise, cornice failures, loose wet, wet slab and isolated deep persistent slab avalanches should be on your radar.
Snowpack Summary
On Tuesday between 25 and 45cm of new snow fell with highest accumulations noted in the south of the region. Extreme westerly winds throughout the storm promoted continued cornice growth and created a widespread wind effect at higher elevations. About 35-60cm below the surface you'll find a widespread hard melt-freeze crust that formed as a result of last week's warm weather and more recent cooling. A few deeply buried weak layers exist within the snowpack including a widespread crust/facet layer buried in early February down around 1.5 m and weak basal facets at the bottom of the snowpack. The near-surface crust has dramatically limited the reactivity of these destructive old layers; however, they have the potential for isolated yet very large avalanches with forecast warming and solar radiation.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.