Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Thursday
Weather Forecast
Thursday: Moderate precipitation continuing overnight / moderate westerly winds / freezing level at 1600m Friday: Light precipitation with locally moderate accumulations continuing overnight / moderate westerly winds / freezing level at 1700m Saturday: generally clear skies / light and variable winds / freezing level at 1900m
Avalanche Summary
On Sunday, a very large (size 3) naturally-triggered avalanche was reported on an east aspect at 2700 m that initiated on the late March crust and then stepped down to glacier ice. More recently, there have been numerous loose snow avalanches running on steep solar aspects to size 2.5. With forecast weather, I expect a shift from wet snow avalanches to storm snow instabilities at higher elevations, while wet snow instabilities will still exist below treeline.
Snowpack Summary
Melt-freeze conditions exist to about 2100m on all aspects and to ridge top on solar aspects. On shaded aspects higher up, 60 cm of recent storm snow is reported to be generally settling well with recent warm temperatures and generally light winds. However, shears may still exist within the storm snow. Additionally, a crust that formed near the end of March is a concern, particularly on steep, solar aspects. With prolonged warming, there is the possibility for wet slabs to release on this layer, or potentially on deeper layers (including the ground), as melt water starts to percolate through the snowpack. Cornices are large in some areas and drooping with recent warm temperatures.
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.
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.
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.