Regions
Northwest Coastal.
Avalanche danger will rise through the day as the new snowfall accumulates and the wind speed picks up.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Thursday
Weather Forecast
The heaviest snowfalls and strongest winds will be concentrated in the southern half of the region through the forecast period. THURSDAY: up to 10cm new snow overnight and 5-10cm through the day, moderate becoming strong southerly winds, 1000m freezing level. FRIDAY: 10-15cm new snow, strong southerly winds, 1200m freezing level. SATURDAY 10-20cm new snow, moderate to strong southerly winds, 1500m freezing level.
Avalanche Summary
Isolated natural slab activity was reported on Tuesday. Most of these avalanches ran on near surface instabilities in steep, unsupported alpine terrain. However in the far north of the region several natural avalanches on Monday stepped down to the early February crust almost 1m deep. A cornice failure also triggered an avalanche on this layer just north-west of Terrace.
Snowpack Summary
Strong wind from the east has stripped snow from exposed slopes and reverse loaded lee features in the alpine and at treeline. The upper snowpack sits on a crust on all but high elevation north aspects with surface hoar in isolated sheltered and shady locations. Recent snow-pit tests near Terrace produced easy sudden planar failures just below this crust. An older crust buried in early February extends up to about 2000m and can now be found around 50cm to 1 meter down. Some recent avalanches have run on this layer and snow pit tests have observed it failing under moderate loads. The mid pack is generally 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.