Special Public Avalanche Warning for this region. Forecast very warm temperatures, high freezing levels, and strong solar radiation will increase the avalanche danger to HIGH in the alpine during the hottest part of the day.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
A well-developed ridge of high pressure will continue to provide clear skies, light winds, and very warm temperatures for Thursday and Friday. Freezing levels may climb as high as 3000 metres, and there may not be a freeze on Friday morning in some areas. A weak trough will move inland from the coast on Saturday, bringing moderate southwest winds and increasing cloud cover. Some light precipitation may make it into the Interior ranges, however it may be mostly rain as the freezing level should remain at about 2500 metres on Saturday.
Avalanche Summary
On Tuesday numerous solar triggered loose wet avalanches were reported up to size 2.5. On Monday some recent storm slab avalanches were reported releasing from skier triggering up to size 1.0 on north aspects in the alpine. Some natural cornice activity was also reported up to size 2.5 from northeast and easterly aspects in the alpine. Forecast very warm temperatures and high freezing levels are expected to increase natural cornice activity, and may trigger the buried persistent weak layers.
Snowpack Summary
New surface crusts have formed at all elevations on solar aspects, and on all but high alpine shaded aspects. Some areas have reported a new layer of surface hoar growing in high sheltered alpine locations above 2300 metres. Approximately 40-50 cm of settled storm snow sits on a melt-freeze crust buried on Mar. 22. The late February persistent weak layer is an aspect dependant mix of surface hoar, facets and/or a thick crust down around 60-110 cm below the snow surface. Commercial operators continue to see hard sudden planar results in snowpack tests, which suggests that wide fracture propagations are possible. Cornices continue to be described as large and fragile. Expect loose wet avalanches and natural cornice falls with strong solar radiation and significant warming this week. Forecast warming may trigger very large slab avalanches on one of the buried crusts or associated weak layers.
Problems
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.
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.