Solar radiation and rising temperatures will destabilize the snowpack and avalanche hazard can rise quickly. Check out the new blog post for this region: www.avalanche.ca/blogs/VTAw_CcAAIUPxFdk/south-coast-problems
Confidence
Fair - Due to the number of field observations
Weather Forecast
A dominating high pressure ridge is building over Southern BC. This will bring summer-like temperatures through the weekend with alpine temps rising to 12 degrees! Saturday and Sunday will be mostly sunny skies with few clouds. Alpine temperatures rising to 8-12 degrees and freezing levels near 2900 m. Ridgetop winds will be light from the WNW. By late Monday, the ridge starts to break down allowing a more seasonally westerly flow.
Avalanche Summary
On Thursday, numerous solar triggered natural loose wet avalanches up to size 1 were reported. A natural cornice failure size 1 also occurred and did not pull a slab from the slope below. With warming and periods of intense solar radiation avalanche danger will rise, solar triggered slab avalanches, failing cornices and loose wet avalanches will likely 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 the April 10th persistent weak interface including crusts, facets and spotty surface hoar on high, northerly aspects. 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.