Confidence
Fair - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Synopsis: Initially, a ridge of high pressure will bring dry, sunny weather for Sunday with increasing cloud through Monday. On Tuesday afternoon, a Pacific frontal system will bring precipitation to the region.Sunday: Dry and mostly sunny. Freezing level going as high as 2300 m. Light northerly winds.Monday: Should stay dry with cloud cover increasing through the day. Freezing level dropping to around 1000 m. Generally light winds, but westerly gusts to 60km/h at ridgetop are possible.Tuesday: Up to 10 cm new snow starting late in the day. Freezing level around 1200 m. Moderate or strong southwesterly winds.
Avalanche Summary
There are important differences in avalanche activity depending on whether you are in the north of the region or in the south. For the south, large avalanches ran during the recent storm, but activity appears to have subsided relatively quickly due to warm temperature and higher snowfall amounts. In the north, where the lower snow amounts have left weak layers more intact, reports continue of rider-triggered and remote-triggered avalanches up to size 2.5. These appear to be failing particularly where a crust lies buried under the upper slab and have been reported from treeline and alpine elevations.
Snowpack Summary
The most recent storm, which ended Friday morning, brought widely varying snowfall amounts to the region, with 30cm in the north end and up to 90cm in the south. Consistent southerly winds during the storm period built windslabs in lee terrain and helped grow cornices.Recently buried surfaces (the Feb. 3 interface) include old windslabs and sun crusts. The new snow is bonding reasonably well at this interface in most locations with the highest concern being the bond to crusts on south and west facing terrain. The January 23rd interface (crusts, facets and surface hoar crystals) lingers in isolated locations. This layer seems to be rounding and bonding under current conditions, but we have reports of a recent size 2.0 releasing on this layer. The mid pack is generally well settled with the average snowpack depth at treeline around 180 cm.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.