Solar radiation and rising temperatures will destabilize the snowpack and avalanche hazard can rise quickly. Watch overhead hazards like cornice fall. Loose wet sluffing and solar triggered slab avalanches.
Confidence
Fair - Due to the number of field observations
Weather Forecast
A pacific front hits the North and Central coast Thursday evening and then slides south towards the South Coast. Confidence is poor with determining how far this storm will track south. Lingering cloud, sunshine and periods of convective snowfall may occur on Friday. Ridgetop winds will be light from the SW and freezing levels near 2000 m. Friday evening a warm ridge builds over the province bringing sunny and dry conditions into early next week. Saturday and Sunday freezing levels will be steady near 2700 m with intense solar radiation and ridgetop winds remaining light.
Avalanche Summary
On Wednesday, natural cornice fall was reported, pulling thin slabs up to size 1 from the slopes below. Strong solar radiation and warming expected through the forecast period. This will likely initiate a natural avalanche cycle. Watch overhead hazards like cornice failures and solar induces loose wet, and slab avalanches.
Snowpack Summary
Anywhere from 20 to 50 cm of recent storm snow sits on a persistent weak layer comprising of crusts, surface hoar and facets which were buried April 10th. Moderate to strong south west winds are redistributing the storm snow into wind slabs on leeward slopes and terrain features. The mid-March persistent weak layer of facets on a crust is now approximately 50-100 cm down and continues to sit dormant. There is a low probability of triggering this layer, however; if it is triggered the consequence would be high. Large looming cornices may become weak with solar radiation and daytime warming. If a cornice fails it could trigger a large avalanche from the slope below.
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.