Regions
Northwest Coastal.
New snow, strong winds, and a warming trend may create touchy storm slabs. These slabs could be sitting on wind slabs formed by the recent outflow winds. Conservative terrain choices are recommended.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
FRIDAY NIGHT: Snowfall, accumulation 10-20 cm, moderate to strong southwesterly wind, alpine temperature near -10 C, freezing level below valley bottom.SATURDAY: Cloudy with light snowfall or freezing rain, accumulation 10 to 20 cm, moderate to strong southwesterly winds, alpine temperature rising to 2 C, inversion conditions with cold valley air and above-freezing level between about 1200 m and 2500 m.SUNDAY: Mostly cloudy with light precipitation in the morning, accumulation 5 mm, moderate to strong southerly winds, alpine temperature near 5 C, freezing level near 2500 m with inversion conditions.MONDAY: Mostly cloudy, moderate to strong southerly winds, alpine temperature near 4 C, freezing level near 2000 m with inversion conditions.
Avalanche Summary
Small naturally triggered wind slabs were observed on Thursday, along with other signs of instability such as cracking. The slabs were observed on all aspects due to varying wind directions in the past few days.
Snowpack Summary
The snowpack is variable across the region. Wind slabs and storm slabs are found on some slopes in the alpine and at treeline. Strong outflow winds have formed wind slabs on southerly and southwesterly lee features at all elevations.Up to 45 cm recent snow overlies several layers of interest in the upper snowpack. These include crusts, surface hoar and facets. A hard crust with associated facets from mid-December sits deeper in the snowpack, about 60 cm down. Any of these layers could create a persistent slab problem if new snow, wind-loading or warming change the properties of the slab above.The lower snowpack is generally strong, with the exception of areas around Stewart and further north where a basal crust and facets exist.
Problems
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.