Regions
Northwest Coastal.
The heaviest snowfall will likely be confined to the coast with the approaching system. The avalanche danger could be slightly lower in areas that receive less than 20 cm of new snow through Sunday.
Confidence
Fair - Intensity of incoming weather is uncertain on Tuesday
Weather Forecast
Synopsis: The active weather pattern continues into next week with a series of frontal systems affecting the region with short breaks in between each pulse.Overnight and Sunday: The first system arrives late Saturday bringing 10-15 cm overnight, and an additional 10-15 cm on Monday morning. The freezing level is around 600 m and winds are strong from the southwest. Monday: Cloudy with sunny breaks. The freezing level is near valley bottom and winds ease to light from the northwest. Tuesday: The next system arrives bringing 5-10 cm of snow and increasing winds.
Avalanche Summary
Several natural slab and loose wet avalanches up to size 2 were reported on Friday. There was also a report of a couple intentionally triggered slab avalanches up to size 2 that were 80 cm deep. Observations are generally limited to below treeline due to poor weather.
Snowpack Summary
Up to 100 cm of storm snow has fallen over the past few days. The new snow was reported to be dry and low density with no notable weaknesses. Deep and dense wind slabs have likely formed in exposed lee terrain and cross-loaded gullies. This new snow fell on a crust, old wind slab, and/or surface hoar depending on aspect and elevation. Most areas are reporting that the snow has bonded well to the underlying melt-freeze crust. Cornices that now loom over many features may become weak with continued growth and/or daytime warming. The mid and lower snowpack layers are generally well settled and strong.
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.
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.