Though we are not completely into spring snowpack conditions, solar radiation and daytime heating will be the big factors on Sunday. It is time to start early and finish early. Don't underestimate the de-stabilizing affects of the April sun.
Confidence
Good - Timing or intensity of solar radiation is uncertain
Weather Forecast
A sunny and relatively calm morning is expected on Sunday with intense solar radiation and rising temperatures. Convective flurries are likely in the afternoon.
Avalanche Summary
A few loose dry slides were observed today on steep N and E aspects up to size 2.0. Also, some small loose wet avalanches occurred on sunny slopes in the afternoon. A very large slide (size 3.5) occurred sometime on Friday in the Tyrwhitt region. This avalanche failed on both the February surface hoar and the basal facets and destroyed approximately 2 Ha of mature forest. It is quite possible that we will see large avalanches as we transition to spring due to a deeper than average snowpack and two concerning deeply buried weak layers.
Snowpack Summary
No new snow overnight, but lots of low density snow is available for transport. Wind loading is occurring at alpine and treeline elevations on lee slopes. On E, S and W aspects crusts are forming each evening and melting each day. The extent of melting is related to the amount of radiation and the air temperatures. Dry snow remains on N aspects above 1900m in most locations. The snowpack is settling. The deeply buried February surface hoar and basal facets are sporadically active in large natural avalanche events, including some triggered by cornice failures.
Problems
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.