Regions
Northwest Coastal.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Tonight and Sunday: Periods of snow, heaviest overnight – 10-25 cm. The freezing level could climb to 1200-1500 m in the south, but remain near valley bottom in the north. Winds are moderate to strong from the W-SW. Monday: Periods of snow – 15-20 cm. The freezing level lowers to around 800-1000 m. Winds remain moderate to strong from the SW. Tuesday: Cloudy with flurries. The freezing level is near 1000 m.
Avalanche Summary
Numerous loose wet avalanches up to size 2.5 were observed on Friday at lower elevations, primarily in the southern half of the region. Fresh deposits were also observed in the Shames backcountry, with some paths running all the way to the valley bottom.
Snowpack Summary
Southern Sections: The latest storm dumped 50-80 cm under mild temperatures and strong SW-NW winds. Much of the low elevation snowpack was washed away by heavy rain, as freezing levels peaked close to 2000 m in some areas. In the wake of the system there was brief clearing and cooling. This may have created a surface crust at lower elevations. Recently buried weaknesses of surface hoar and/or facets are now well over 1 m deep and were likely flushed out or squashed by the heavy snowfall. Northern Sections: Storm snow totals are closer to 30-40 cm. Fresh dense wind slabs are likely in exposed lee terrain and cross-loaded features. A recently buried surface hoar layer is now down around 50-60 cm and is likely primed for rider triggering. A facet/crust layer exists near the base of the snowpack, primarily on higher NW through E facing slopes. Triggering this layer may be unlikely, but if triggered the resulting avalanche would be very large and dangerous.
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.