The first big Spring warm-up occurred today producing isothermal snow and a large avalanche cycle up to size 3.0. An approaching cold front will cool things down, but the sun will shine Wednesday. Avoid all avalanche terrain when the snow is moist.
Confidence
Good - Timing or intensity of solar radiation is uncertain
Weather Forecast
A cold front will move into the region tonight and cool the temperatures. As much as 8cm of new snow is possible overnight. Wednesday will bring a mix of sun and cloud, strong west winds and Alpine temperatures near -6 degrees. Freezing levels should only reach 1300m.
Avalanche Summary
A widespread natural cycle up to size 3.0 was triggered by warming and solar radiation. Both loose wet and loose slab avalanches were observed today. Most of the slides stepped to ground.
Snowpack Summary
Spring conditions. Isothermal snow below treeline on all aspects and on solar aspects at all elevations. Numerous loose wet and loose slab avalanches up to size 3.0 had occurred by midday. Wind slabs are present in Alpine and Treeline terrain on lee and cross-loaded features. Cornices are sagging.
Problems
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.
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.