Regions
Northwest Coastal.
The weather over the next few days will deliver an interesting mix of winter and spring-like conditions. Brief periods of solar radiation may continue to wreak havoc on Monday, so make sure your travel plans allow for changing conditions.
Confidence
Moderate - Wind speed and direction is uncertain on Monday
Weather Forecast
10-15cm of new snow is expected between Sunday night and Monday morning. On Monday, expect mainly cloudy skies, light snowfall and the odd sunny break. Heavy mixed rain and snow (up to 40mm each day) is forecast for Tuesday and Wednesday. Ridgetop winds should be moderate from the southwest on Monday, and then become strong with Tuesday and Wednesday's storm. Freezing levels will yo-yo from 1500m on Sunday night to about 1200m by Monday afternoon and Tuesday morning. From there, the freezing level will gradually spike to about 1750m by Wednesday evening.
Avalanche Summary
Over the past week, loose wet avalanches, cornice failures, and deeper persistent slab avalanches to size 3 were observed failing naturally in response to warming and solar radiation. With forecast snow and wind, we are shifting back to a general pattern of storm slab avalanche activity. That said, spring-like loose wet avalanches, isolated persistent slab avalanches and cornice failures will still be possible at elevations where precipitation falls as rain or during periods of warming and solar radiation.
Snowpack Summary
By Monday morning, light to locally moderate amounts of new snow are expected to overlie a widespread melt-freeze crust. Below about 1300m, light rain is expected to further saturate the snowpack keeping the snow loose and unconsolidated. The warm temperatures and sun over the last week woke-up deeply buried weak layers within the snowpack. These includes a weak crust/surface hoar layer which was buried down 30-40cm in the north of the region, a widespread crust/facet layer buried in early February down around 1m, a lingering surface hoar layer from January down over a meter, and weak basal facets at the bottom of the snowpack. Cooling should dramatically limit the reactivity of these old layers; however, they may come back to life during future periods of warming, heavy rain or solar radiation.
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.