Regions
Northwest Coastal.
Spring conditions typically means the hazard is highest during the heat of the afternoon. Cornices and loose wet sluffing are spring problems which can be expected on Saturday. Wind slabs may also still be lingering in high elevation leeward terrain.
Weather Forecast
A mix of sun and cloud is expected for Saturday. Alpine winds are forecast to be moderate from the northwest in the morning and ease in the afternoon. Freezing levels are expected to climb to around 2200m. A mix of sun and cloud is expected for Sunday with light alpine winds and afternoon freezing levels around 2000m. Mostly cloudy conditions are forecast for Monday with light scattered flurries and afternoon freezing levels around 1500m.
Avalanche Summary
Data has become very limited for the region as we move into the spring and a lack of reported avalanche observations does not mean avalanches are not occurring. On Thursday, a natural size 3 icefall was reported north of Stewart on a south aspect at 1800m. On Wednesday, loose wet avalanches were reported on sun exposed slopes and glide cracks are reported to be moving and opening. Over the weekend, loose wet sluffing is expected on steep sun exposed slopes and cornices will become weak with daytime warming and sun exposure. Lingering wind slabs may still be reactive in exposed high elevation terrain.
Snowpack Summary
A moist or wet surface snow is being reported on all aspects at all elevations. A surface crust is expected to form Friday overnight as temperatures drop but this crust may break down during the day with warm temperatures and sun exposure. A widespread crust layer from the last period of major warming sits below the storm snow from earlier in the week. This snow is reported to be settling rapidly and generally bonding well to the crust below. Prior to the current warm conditions, strong southerly and westerly winds promoted cornice growth and formed wind slabs. These wind slabs may still be lingering in leeward terrain features at the highest elevations. 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 and they have become dormant; however, they have the potential for isolated yet very large avalanches with prolonged periods of 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.
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.
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.