Weather Forecast
A very benign weather pattern will bring little precipitation, convective cloud, light winds and sunny periods over the next few days. Saturday: Scattered convective cloud cover. Light flurries, with no significant accumulations. Ridgetop winds light from the NW. Alpine temperatures near -1. Freezing levels 1700m falling to valley bottom at night. Sunday/Monday: A dominating ridge with diurnal temperature swings and freezing levels rising to 2000 m during the day. Continued sunny skies, and light ridgetop winds. The ridge will weaken on Monday allowing bands of cloud, and light precipitation.
Avalanche Summary
Observations from the past few days are limited. On Thursday a natural cornice release size 2.5 was reported. This did not pull out a slab on the slope below. On Wednesday reports include one natural cornice triggered Size 2.5, 100cm thick wind slab avalanche on a north aspect. A couple days ago, a size 3 glide slab avalanche was also observed on a south aspect at 1800m. I suspect natural activity will occur throughout the weekend with warming temperatures, and sunny skies. Make observations continually as you travel. Pinwheeling, snowballing, loose sluffing, and avalanches are all indicators of the snowpack deteriorating. I would avoid slopes where these actions are occurring.
Snowpack Summary
Over the past week up to 60 cm of recent storm snow has fallen. Sustained southeasterly through northeasterly winds are contributing to continued wind slab formation as well as cornice development at upper elevations. Although generally settling and bonding well, recent snowpack tests on a north facing treeline slope resulted in easy to moderate shears down 25cm within the storm snow, and down 65cm on an underlying crust that formed near the end of March. Not only will daytime warming and sun-exposure cause surface snow to lose cohesion and cornices to weaken, they will also increase settlement rates and decrease slab stability.
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.
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.