Storm slabs may remain reactive to human triggered where they bond poorly to the underlying hard surface.
Watch for fresh wind slabs forming as northerly outflow winds cross- and reverse-load atypical terrain features.
Cornices may have grown significantly with wind and snowfall over the weekend. Be especially mindful of overhead cornice hazard if the sun comes out and the storm snow is experiencing strong solar radiation for the first time.
A weak layer formed in late January may be found 50 to 150 cm deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.
Reactivity on this layer has tapered, but the significant amount of new load over the weekend may cause this layer to 'wake up'.
The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Terrain features to be suspect of include the lee side of ridges, openings in trees, cut blocks, and burns, especially on northerly aspects where the layer may not be capped by a firm crust.
This weekend's storm brought 30-100 cm of storm snow overlying the February 15th drought layer. Reports suggest that the storm snow is bonding poorly to this interface and human-triggering could persist into Tuesday.
Expect to find deeper, and stiffer slabs to exist in wind-loaded terrain. Northeasterly outflow winds may have created wind-loaded pockets in more atypical, reverse-loading patterns and at lower elevations than you might usually expect.
Dry-loose avalanches may be seen from steeper slopes, especially where a firm crust exists below the new snow.
Bundle up in your warmest gear, arctic air is here!
Monday Overnight: Clear skies. Alpine temperatures around -25 C. Light to moderate northeasterly winds.
Tuesday: Cold and clear. An alpine high of -20 C. Light northeasterly winds.
Wednesday: Mainly cloudy with light snowfall. Winds shifting northwest and strengthening moderate to strong. Alpine temperatures rising to -15 C.
Thursday: Partially cloudy, light flurries. Light to moderate northwest winds. Alpine temperatures around -15 C.
Sunday was an active day for avalanche activity! Numerous human-triggered storm slabs and wind slabs were reported at all elevations throughout the region, with many of these avalanches failing on the mid-February drought layer. Several natural wind slab, storm slab, and dry loose avalanches occurred, some as a result of cornice failures.
Also on Sunday in the north of the region, a cornice-triggered storm slab avalanche stepped down to the mid-January interface on an east aspect in the alpine, reminding us that this layer is still with us and has the potential to be triggered with larger loads.
During the peak of the storm on Saturday, numerous natural and human-triggered storm slabs were reported on all aspects due to rapid loading. Larger natural and human-triggered wind slab avalanches were reported in wind-loaded terrain in the alpine and treeline. Several natural dry loose avalanches were reported out of steep terrain on all aspects.
Explosive control last week initiated some larger persistent slabs up to size 3.
Last weekend's storm brought 20-80 cm of new snow accompanied by southwesterly winds. Below 1200 m the majority of the precipitation fell as rain, with 10-20 cm of snow now overlying a thick melt-freeze crust.
Up to 120 cm now overlies the mid-February drought layer. This layer is comprised of surface hoar in sheltered areas, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. In many areas, the storm snow is bonding poorly to this firm layer.
The mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. This layer has not been reactive to skier traffic in the past week but continues to show reactivity in snowpack tests. With a significant amount of new snow, this layer could start to 'wake up' or be triggered from a large load like a cornice fall or a shallower slab avalanche stepping down to this layer.
The facet/crust layer that formed in early December is now buried around 150 to 250 cm. Human triggering of this layer is unlikely, except perhaps on a re-loaded bed surface or in a shallow snowpack area. This layer may become a concern during periods of warming or heavy loading.
