Overhead hazards, such as large avalanche paths and cornices will be a major concern over the next few days. Sporadic, very large natural avalanches may run full path to valley bottoms. Avoid all avalanche terrain during periods of rapid warming.
Weather Forecast
SUNDAY NIGHT: Clear / Light, northeasterly winds / Alpine low -2 / Freezing level 1500 m.NOTE: Sunday night is the last night of the forecast period that freezing levels are expected to drop at night. This will significantly increase the impact of day time warming on the snowpack.MONDAY: Sunny / Light, northeasterly winds / Alpine high 4 / Freezing level rising to 2700 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 6 / Freezing level rising to 3000 m.WEDNESDAY: Sunny / Light, southeasterly winds / Alpine high 7 / Freezing level 3000 m.
Avalanche Summary
On Saturday, several naturally triggered, persistent slab avalanches up to size 3 were reported on a variety of aspects in the alpine. Natural avalanche activity and size of avalanches are expected to increase during the next few days.On Friday, a natural size 2.5 and explosive triggered size 3 persistent slab avalanches were reported on north aspects in the alpine. Human triggered persistent slab avalanche activity is expected to increase with the forecast sunshine and rising freezing levels.
Snowpack Summary
15-30 cm of recent storm snow is sitting on a pile of facets (sugary snow), as well as a crust on sun exposed slopes. The recent storm snow has settled into a cohesive slab and is ripe for human triggering. This persistent slab is currently our primary concern.At lower elevations a weak layer of surface hoar (weak, feathery crystals) buried in mid-January can be found approximately 50-90 cm deep and may be combined with a crust on south facing slopes. This layer has recently been unreactive, however, the forecast warming event may awaken this layer in low elevation areas such as steep cutblocks and large open glades.The base of the snowpack is composed of facets (weak, sugary snow) that sit on a crust. Very large avalanches failing on this persistent weak layer will become more likely with the forecast sunshine and rising freezing levels.
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.
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.
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.