Regions
Northwest Coastal.
Fresh storm slabs will be reactive to human triggers at higher elevations. Use extra caution on south-facing slopes when the sun is out.
Confidence
Moderate - Due to the number and quality of field observations
Weather Forecast
WEDNESDAY: Mostly sunny, light wind, freezing level up to 600 m, alpine high temperatures near -8 C.THURSDAY: Snow starting in the morning with 4-8 cm accumulations by the afternoon, strong south wind, freezing level near valley bottom, alpine high temperatures near -10 C.FRIDAY: Continued light flurries with another 5 cm of snow, moderate south wind, freezing level up to 600 m, alpine high temperatures near -8 C.
Avalanche Summary
Preliminary reports from Tuesday suggest some avalanche activity likely occurred at higher elevations during the storm.No new avalanches were reported on Monday and activity on Sunday was limited to a few small loose avalanches on steep sun-exposed slopes.Last week, large persistent slab avalanches were reported on east to northeast aspects at all elevations. These were failing on the early-March and mid-March layers.
Snowpack Summary
10-30 cm of new snow sits above a variety of crusts on all but high north aspects.In the south of the region, 70 to 90 cm of snow overlies two layers of surface hoar. The layers are most prominent on north to east aspects and were buried early-March and mid-March. In the north of the region, these layers are around 40 cm deep.Shallower parts of the region, such as the far north, have weak sugary facets near the bottom of the snowpack.
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.