Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Thursday: Cloud turning to flurries in the afternoon as a weak system approaches the coast. 10-15cm possible overnight. Alpine temperature near -3C. Moderate southerly winds.Friday: Light snowfall. Temperatures dropping in the afternoon. Moderate southerly winds veering to north-westerly in the evening. Saturday: Alpine sun and low level cloud. Light westerly winds. Westerly upslope showers possible, easing by afternoon.
Avalanche Summary
Over the last few days, warming and sunshine have triggered avalanches up to size 2.5. Most have been on sunny slopes, but some north aspects became unstable at low elevations and also released. Sporadically, avalanches have failed on the Jan 20th layer with large triggers, like cornice fall. Isolated wind slabs have been triggered by skiers on steep rolls near treeline.
Snowpack Summary
Variable wind slabs have been reported. A melt-freeze cycle has created a crust which is harder and thicker the lower in elevation you go. On north aspects in the alpine, near surface facetting has kept snow dry and loose. Surface hoar of size 1-4mm is likely to get buried by incoming snow on Thursday night. A facet layer buried on Jan 20th still exhibits hard, sudden planar results in isolated snowpack tests and avalanches are occasionally failing on this layer with large triggers. It's about 120-150cm deep in the snowpack. Large cornices have the potential to act as a trigger for deep avalanches on the slope below.
Problems
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.