Touchy wind slab conditions exist. Conservative route selection is advised.
Weather Forecast
Tuesday will be cloudy with sunny periods and isolated flurries. Only minimal snowfall accumulations are expected. Temperatures should reach a high of -5 °C in the Alpine with ridge-top winds out of the west at 35 km/h gusting to 90 km/h. Wednesday and Thursday could see snowfalls in the 20cm range with strong SW winds.
Avalanche Summary
A moderate sized avalanche cycle is on-going related to the recent persistent strong Northerly winds. Natural avalanche activity up to size 3.0 (average size 2.0 to 2.5) occurred today in specific Alpine terrain. Most slab avalanches occurred immediately below ridge crests under cornice features, or were triggered by loose dry avalanches from very steep alpine terrain. Fracture lines ranged from 50 to 100cm deep. The activity occurred on NE, E, S and SE aspects at elevations of 2400m and above. In addition, solar triggered slides up to size 1.5 occurred in the afternoon on steep S, SW and W aspects.
Snowpack Summary
An additional 12cm of new snow overnight brings recent storm snow totals to 20 to 30cm at Treeline. Alpine and upper Treeline areas continue to see wind slab development on NE, E, SE, and S aspects due to persistent winds that have been out of the North for the past 2 days. An avalanche cycle due to wind loading is on-going (see avalanche discussion). Moist snow was observed on steep solar aspects in the afternoon. Cornices have grown significantly over the past 48 hours. Test profile at 2350m today shows easy shears at the storm snow interface, moderate shears down 40cm at an old wind slab interface and hard shears down 115cm on a layer of facets. The Jan 6th interface buried 80cm did not produce a shear in our tests today.
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.
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.