Regions
Northwest Coastal.
Confidence
Fair - Freezing levels are uncertain on Saturday
Weather Forecast
Between friday night and saturday morning 30-40cm of snow and strong southwest winds are forecast for the region. Freezing levels for this period are expected to rise to 1600m.A clearing trend is forecast for saturday afternoon and into sunday as winds eventually switch to light and northerly and freezing levels fall to surface.The clearing will be short-lived as more heavy snowfall and strong southwest winds will resume on sunday afternoon and into monday. Freezing levels on monday to sit at about 500m.
Avalanche Summary
Control work with explosives over the last few days has produced numerous avalanches up to size 2.5 on a variety of aspects and elevations. On Wednesday widespread natural avalanches up to size 2 were reported. These avalanches all ran on the mid-December buried surfaces ( surface hoar, melt-freeze crusts). With more wind, snow and rising freezing levels Friday/Saturday we can expect another significant natural avalanche cycle.
Snowpack Summary
The southern part of the region has received up to 60-80cm of snow over the past 5 days (Kasiks, Terrace areas) and less snowfall to the north. This is forming storm slabs at all elevations. This new snow is being blown around by strong southwest winds creating new wind slabs on lee slopes. Buried beneath the new snow sits a variety of weak snow surfaces (surface hoar, melt-freeze crusts, and facetted snow). This crust is up to 20cm in thickness and extends up to alpine elevations in the south, and around 1000m in the north. The surface hoar growing on the crust was sized up to 10mm. A strong temperature gradient in the top 30cm was reported to be faceting snow below the surface crust. These layers have met their threshold, and while widespread avalanche activity has occurred lots more is expected with the forecast weather. Forecast rain for lower elevations will probably mean further weakening of the snowpack for the short term and another rain crust (sliding layer) for the future. The mid and lower snowpack are well settled and strong.
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.