Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Thursday: Moderate precipitation starting overnight Wednesday becoming light by Thursday / moderate westerly winds / freezing level at 1700m Friday: Light precipitation with locally moderate accumulations / moderate westerly winds / freezing level at 1700m Saturday: generally clear skies / light and variable winds / freezing level at 1900m
Avalanche Summary
Over the past few days, many wet loose snow avalanches to size 2.5 occurred in response to daytime warming and direct solar radiation. Numerous size 2-3.5 slab avalanches also occurred on sun-exposed aspects, with more isolated activity on shaded aspects. There has also been an increase in glide crack activity (mostly below treeline) to size 3.5. 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
Up to 80cm of snow overlies a layer of facetted crystals sitting on a crust in the alpine and at treeline. Recent naturally triggered avalanches are noteworthy and suggest the problem still exists. Wind slabs are reported to be isolated to the immediate lee of exposed features at high elevations. Melt-freeze conditions exist on all sun-exposed slopes as well as many north facing areas with limited crust recovery developing at night. There is still concern for the mid-February buried surface hoar layer that is down about 140-220 cm.; however, avalanches releasing on this layer represent a low probability-high consequence scenario. Cornices in the region are very large. With warmer temperatures and longer periods of direct solar radiation, these are likely to become weak and fail. They could provide a large enough trigger to release these deep layers on slopes below.
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.