At upper elevations, especially on east, south, or west aspects where the dry snow sits on a crust, storm slabs have been propagating widely, are surprisingly deep, and could be triggered by warmth, cornices, or riders. Reports of whumpfing from the west side of the Purcells are noteworthy and worrisome!
Reports of whumpfing are noteworthy; the snow remains sensitive and it seems remotely triggered avalanches are possible. This snow is being triggered by day time warming, failing cornices, or riders, and it's propagating widely.
Surface snow will destabilize and may avalanche naturally with daytime warming and especially with solar exposure.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth.
Suspect terrain includes steep, shallow, and rocky terrain where the snowpack varies beween thin and thick.
Friday's reports show the weak layers, up to 80 cm below the surface, were reactive to explosives, skiers, and naturally. Sizes were between 2 and 3.5. Additionally, there are stories about whumpfing around moraines. Explosives targetting the deep persistent layer at the bottom of the snowpack released several size 3.5 avalanches up to 200 cm thick.
Search and Rescue responded to a serious incident today, Saturday April 15, in the Thunderwater Lake riding area: a rider triggered size 3 avalanche on a southeast facing alpine slope with a crown 40 to 100 cm thick.
Thursday's avalanche reports spoke to the continued storm slab or persistent slab avalanche problem (previous dry snow above crusts or facets from April 7 or March 31) with several avalanches to size 3.5, many seemed to release with daytime warming. Some were cornice triggered.
A serious avalanche incident occurred in the backcountry just east of Revelstoke on Wednesday. Details are available here. This is representative of the "recent storm snow above a crust" problem.
Looking forward, the need for backcountry travelers to manage a wide range of avalanche concerns that vary by elevation and aspect continues.
At the surface crusts have formed on solar aspects and surface hoar is growing on shady aspects. At high elevations (where winter remains and the snow is dry) around 30-60 cm of previous storm snow is settling and remains dry (at least on shady terrain).
Recent snow overlies two lingering weak layers: a widespread melt-freeze crust buried April 7 and a layer of faceted snow or surface hoar buried April 1. Whumpfs and numerous recent avalanches, some with wide propagation, are attributed to these lingering problem layers.
The mid-snowpack is strong. However, November depth hoar remains at the base of the snowpack and remains a concern in rocky, shallow, variable depth snowpack areas at treeline and above.
Saturday Night
Cloudy with clear periods and isolated flurries. Only a trace of new snow. Freezing level falling to around 1200 m. Light to moderate south wind.
Sunday
Cloudy with sunny periods and showers during the day. New snow around 2 - 5 cm but possibly as much as 10 cm south of Revelstoke. Freezing level around 2100 m. Light to moderate southwest wind. Treeline temperatures around 0 C. Snow picks up after the sun sets with up to 15 or 20 cm of snow (favoured areas are south of Revelstoke and the west side of the Purcell Mountains) by Monday morning.
Monday
Cloudy with sunny periods and an additional 2 to 5 cm accumulating. Again, highest accumulations in the south. Freezing level around 1700 m and treeline temperatures around -5 to -10 C. Light to moderate westerly winds.
Tuesday:
A mix of sun and cloud with flurries. A trace to 5 cm of new snow. Freezing level around 1700 m and treeline temperatures around -3 to - 8 C. Light southwest winds.
More details can be found in the Mountain Weather Forecast.
