Spring weather conditions are slowly starting to transform the snowpack. Avalanche danger will rise rapidly during periods of intense solar radiation and rising freezing levels.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
The region could see 5cm of new snow overnight, with Sunday bringing a mix of sun and cloud and isolated flurries. Temperatures are a bit milder than we have had recently with highs in the Alpine of -4 °C and the freezing level near 2200m. Winds will be moderate from the west. Conditions will remain unsettled into the early part of the week.
Avalanche Summary
A few loose wet avalanches up to size 1.5 occurred this afternoon on steep solar aspects.
Snowpack Summary
Warm temperatures and mostly sunny skies on Saturday led to moist snow on solar aspects at all elevations and at lower elevations on polar aspects. Wind slabs in the Alpine are highly variable in distribution and density, but are most commonly found near ridgelines in lee and cross-loaded terrain. On steep solar aspects in the Alpine there is a 30 to 50cm thick slab overlying the March 15th crust, and though this condition is not widespread there has been some avalanche activity associated to this problem recently. Cornices are large, are feeling the heat of the April sun, and should be avoided.
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.
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.