Winter marches on at higher elevations. Wind slabs and cornice falls are the most likely problems. Persistent layers continue to exist in the snowpack, and may become reactive during periods of strong sun or daytime heating.
Weather Forecast
Overnight: 5-8cm of new snow with light westerly winds and freezing down to 600 metres. Tuesday: Another 3-5 cm of new snow with light south winds and daytime freezing up to 1400 metres. Wednesday: A mix of sun and cloud with periods of convective flurries. Daytime freezing up to 1700 metres. Thursday: 5-8 cm of new snow with light southeast winds and daytime freezing up to 1600 metres.
Avalanche Summary
Loose dry and loose wet avalanches to size 1.0 were reported on Sunday. Saturday's reports included details of one Size 2.5 deep persistent slab triggered by a large cornice fall on a north aspect in the Valhallas. Numerous storm slabs were observed releasing naturally in various areas of the region from Size 1.5-2.5, with crown fractures ranging from 30-50 cm and north to northeast aspects seeing the majority of this activity.
Snowpack Summary
5-10 cm of new snow has added to the 30-40 cm of recent snow that blanketed upper elevations of the region late last week. The recent snow sits above a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. Fragile new cornice growth also occurred along ridgelines over the course of the week. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. Yet another deep release was reported in the region on Saturday. This activity, although growing more sporadic, is keeping these layers an ongoing concern. They may be more likely to fail on southerly aspects during periods of strong solar radiation.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
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.
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.