Regions
Northwest Coastal.
Weather Forecast
If you've been following these forecasts over the past couple of days, you probably noticed that they were off by a fair bit. Tom Riley does a good job of explaining the situation in his Blog on 'Blowing the Forecast' from Jan. 24th (link below). The current forecast is calling for precipitation easing throughout the day on Friday with 10mm expected for the western (upslope) side of the ranges. A ridge of high pressure is expected to keep the region dry Saturday and Sunday. Freezing levels are expected to drop to 1100m by Friday afternoon and remain steady for the weekend. Strong to extreme southwesterly winds are also expected to ease off by Friday afternoon and remain light to moderate for the weekend.
Avalanche Summary
Reports from Wednesday include a few natural wet-loose avalanches up to Size 2 with afternoon warming and solar radiation. Explosive control results were slightly smaller than expected with numerous Size 2.0 to 2.5, 10-40cm thick slab avalanches on all aspects in the alpine, and several large cornice releases.
Snowpack Summary
Total snowpack depths pushing 5m at treeline are at new record levels for this time of year. Recent warm temperatures helped settle storm snow into a touchy surface slab at lower elevations. Other weaknesses within the upper snowpack and the Jan. 20th facets down around 150cm, create the potential for large step-down avalanches, but things seem to be settling rapidly. Strong winds associated with recent storms means large weak wind slabs and cornices on lee and cross-loaded terrain. Most snowpack concerns are limited to the surface layers, however large triggers such as cornice falls and smaller avalanche stepping-down could affect deeper weaknesses.
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.