Regions
Northwest Coastal.
Weather Forecast
Overnight Thursday: Snow amounts up to 10cm. As the front weakens on Friday only few flurries are expected. Freezing levels near 1000m. Ridgetop winds will be light from the SW, with alpine temperatures near -3. Saturday/Sunday: A weakening front may bring 2-5cms later Saturday night. Clear, sunny skies and lower freezing levels expected on Sunday.
Avalanche Summary
One natural cornice fall triggered a size 2 on the slope below. Reporting persons mentioned it may be 48hrs old. Suspect the Jan 20th facet layer, which may still be susceptible to large triggers. 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 and Friday. 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.