Special Public Avalanche Warning extended for this region. Continued very warm temperatures with little overnight freeze coupled with 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
The ridge of high pressure that is responsible for the clear skies and very warm temperatures is slowly starting to move eastward. Freezing levels should drop a bit, but will remain above 2500 metres overnight and morning sun should quickly break down any crusts that develop. High cloud is expected to move into the interior ranges by Saturday afternoon. Moderate westerly winds on Saturday night combined with light precipitation may not drop freezing levels more than a few hundred metres, and may inhibit crust formation overnight. Sunday should be mostly sunny with light winds and freezing levels at 2500 metres. Freezing levels should begin to drop by Monday morning, when moderate southwest winds and precipitation move inland from the coast.
Avalanche Summary
On Thursday, solar radiation continued to result in natural cornice falls up to size 2.5 and loose wet avalanches up to size 2.0. On Wednesday, slab and loose snow avalanches were reported up to size 2 on a variety of aspects, mostly triggered by cornices or solar radiation. On Tuesday numerous loose wet avalanches up to size 2.0 were reported, and one of these loose wet slides stepped down to a buried crust down 50 cm and resulted in a size 2.5 on a steep east aspect at 2200 metres.
Snowpack Summary
Forecast warming and strong solar is expected to result in loose wet avalanches on sun exposed aspects at all elevations. This warming trend may start to affect deeper snowpack layers each day. Surface crusts may break down early, and persistent weak layers may fail if the warming reaches their fragile structure. The late February surface hoar/crust layer is down 40-90 cm. This layer may continue to react to human triggers during periods of strong solar radiation and high daytime temperatures. Loose wet avalanches in motion, or cornice falls may step down to deeply buried weak layers. Cornices continue to be described as large and fragile, and may fail with forecast warming and strong sunshine this week. Conservative terrain without overhead hazard is a good strategy for avoiding the persistent slab problem.
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.