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 - Timing, track, or intensity of incoming weather system is uncertain
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 2200 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, solar triggered natural loose wet avalanches up to size 1 were reported. On Tuesday, a skier triggered size 1 storm slab avalanche failed on a NE aspect around 2100 m. The skier was partially buried with no injuries. The avalanche was anywhere from 10-40 cm deep, 10 m wide and 10 m long. With warming and periods of intense solar radiation avalanche danger, weak cornices will likely fail and loose wet avalanches will continue. Be aware of rapidly changing conditions.
Snowpack Summary
Upper elevations have received 25-40 cm of recent storm snow. The new snow sits on a variety of old persistent weak layers including crusts, facets and spotty surface hoar on northerly aspects which were buried April 10th. This interface has shown a poor bond and has been reactive naturally and to human triggers. Moderate to strong south west winds has redistributed the recent storm snow into wind slabs on leeward slopes and behind terrain features. The mid-March pwl is down 100-150 cm and has been producing hard, resistant results in snowpack tests and has sat 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.
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.
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.