Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Wednesday: Cloudy with light precipitation starting in the afternoon. Southerly winds increasing by afternoon. Freezing level around 800m.Thursday/Friday: A series of fronts is forecast to bring light snow to the area (perhaps 15-25mm total, with highest amounts in the north). The timing and amount of precipitation are still uncertain, but the general picture is for precipitation to decrease during Thursday morning and increase again by Thursday evening, with moderate to strong southerly winds. The freezing level should rise to around 1500m by Friday.
Avalanche Summary
Wind loading led to a localized avalanche cycle near Stewart on Sunday and skiers triggered small pockets of slab on convex rolls at treeline on Monday. Several solar-triggered avalanches have been observed on sunny slopes during the heat of the day and warm temperatures led to avalanches, even on shady north aspects, below about 1100m on Monday. A couple of avalanches pulled out the Jan 20 facet layer on Monday with heavy triggers.
Snowpack Summary
Strong outflow winds from the east have created new wind slabs. Recently, temperatures have been unseasonably warm, leading to moist or wet weak surface snow conditions. Where a re-freeze has occurred, a crust now exists. Recent storm snow appears to be well settled. 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. Cornices will be weakest during the heat of the day and 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.