Avalanche danger will rise during the day with intense spring sunshine and warming temperatures. Plan to be off big sun-exposed slopes early before the snow becomes moist or wet.
Weather Forecast
Synopsis: A ridge of high pressure should maintain mainly sunny skies on Saturday and Sunday. Freezing levels should climb to 1500m on Saturday and 1800-2000m on Sunday. Upper level winds are light and variable. An upper level low pressure system should spread more cloud and light precipitation on Monday. The freezing level should hover around 1600-1800m.
Avalanche Summary
New observations include loose-wet avalanches up to Size 2 from steep solar aspects. Reports from Wednesday include natural activity up to Size 3 in response to direct sun-exposure. One natural Size 3, 160cm thick slab avalanche on a steep NE facing alpine glacier was suspected to have failed on the late-March interface. A settlement was felt 1 Km away during this avalanche, which suggests a high propensity to propagate fractures. More evidence of the widespread natural avalanche cycle during the storms earlier in the week was also observed, with slabs up to Size 3.5 running full path.
Snowpack Summary
Over 60cm of new snow in the past couple of days was redistributed by strong southwesterly winds into thick wind slabs. A predominately crusty weak interface from late March, now down 50-150cm, remains a potential failure layer for large slab avalanches, especially with heavy triggers such as cornice falls and step-down avalanches. 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
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.
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.
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.