Regions
Northwest Coastal.
The heaviest snowfall for the next few days is forecast for the extreme southwest corner of the region. Local avalanche danger could be higher in areas west of Terrace and south of highway 16.
Weather Forecast
WEDNESDAY: Cloudy with light to moderate snow – 5-15 cm. The freezing level gradually climbs to 1200-1400 m near the end of the day. Ridge winds are light increasing to strong from the E-SE. THURSDAY: Periods of snow – 10-20 cm. The freezing level dips back to 800-1000 m by the end of the day and winds are moderate from the S-SE. FRIDAY: Cloudy with sunny breaks. The freezing level is around 1400 m and winds are light.
Avalanche Summary
Observations on Monday were limited due to poor visibility; however, there were a few reports of natural slab avalanches up to size 2 from immediate lee slopes in the alpine. There was also a report of a size 3 avalanche that initiated on a north aspect in the alpine, and a large natural cornice fall. Expect wind slabs to remain sensitive to rider triggering in steep exposed terrain.
Snowpack Summary
Over the past few days we've seen snowfall accumulations of 5-15 cm each day, and storm snow totals of around 40-60 cm. Strong to extreme ridgetop winds have shifted the new snow into hard or soft wind slabs at treeline and in the alpine, adding to an ongoing wind slab problem. Some areas are reporting a weak surface hoar layer near the base of the most recent storm snow. An old crust buried in early February can now be found around 80-120 cm below the surface. This crust, which may coexist with small facets or decomposing surface hoar, recently produced sudden planar ("pops") results in snowpack tests. Although no recent avalanches were reported to have failed at this interface, I'd remain suspicious of this layer in steep, unsupported terrain at treeline and in the alpine.
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.
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.