Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday
Weather Forecast
Mostly clear skies are forecast for sunday morning with freezing levels at or near surface. Late in the day another frontal system will hit the region bringing up to 50cm of snow overnight and throughout monday. Strong southwest winds and freezing levels of 900m will accompany this system.Tuesday calls for light to moderate snowfall in the morning, cooler temperatures and reduced westerly winds.
Avalanche Summary
Control work with explosives during the week 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 the intense wind and snow forecast for monday we can expect another significant natural avalanche cycle.
Snowpack Summary
The southern part of the region has received up to 70-90cm of snow over the past 5 days (Kasiks, Terrace areas) and less snowfall to the north. This has formed storm slabs at all elevations. This new snow has been 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 also 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 monday's forecast weather. 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.