Forecast snowfall amounts are enough to create dangerous avalanche conditions for Monday, but surface instabilities will be overlapping several problematic snowpack layers that are consistently being indicated in recent step down and even remotely triggered avalanches. It's a good day to back off from avalanche terrain while the snowpack decides how to react to the latest load.
Numerous problematic weak layers exist in the top meter of the snowpack. Recent large persistent slab avalanche observations are strong evidence that these layers are still an active concern in this region. Recent avalanches have been triggered by a mix of large loads like cornices but also remote triggers.
Continuing, convective snowfall and strong southwesterly winds are building storm slabs and wind slabs that will be reactive to natural and human triggers. Expect wind loaded spots to be particularly touchy.
Keep in mind that storm slabs have strong potential to step down to deeper weak layers, resulting in large and consequential avalanches.
A layer of large and weak facets sits near the base of the snowpack. This layer continues on a sporadic basis to produce very large avalanches that can travel far. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain, or by triggering a smaller avalanche that could step down to this layer. Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.
Among several natural and human triggered wind slabs and storm slabs (as large as size 2.5), Friday and Saturday's reports also included a few notable observations of step down avalanches and remotely triggered avalanches involving persistent weak layers.
On Saturday just west of Frisby ridge, an aircraft remotely triggered a 70 cm-deep persistent slab on a steep roll in a below treeline opening from 100 metres away. On Friday we saw a cornice release that triggered a small pocket to the basal snowpack in the South Monashees while another report from the central Monashees details wind slabs in several instances stepping down to one of several midpack layers covered in our snowpack summary.
It seems right now that any surface avalanche or cornice drop stands a very good chance of stepping down to a weak layer.
Another 15-35 cm of new snow should accumulate in the region by end of day Monday with amounts once again greatest in the north of the region.
The new snow will add to about 60-100 cm of storm snow from the past week, arriving most recently with strong southwest winds. These increasing storm totals are sitting above wind-affected surfaces and a crust that extends up to 1800 m in the northern part of the region and up to 2000 m further south. Small facets may be found above the crust. This layer warrants close monitoring as we move through the period where a critical load and slab properties may develop over it.
Deeper in the snowpack two layers of surface hoar which formed in early January are now roughly 80 to 140 cm deep. Although snowpack tests are indicating strengthening here, these weak layers are still being watched closely by local operators and may be associated with recent isolated step-down avalanches.
Large and weak facets from November are near the base of the snowpack and although avalanche activity on this basal weakness has been on a bit of a decline, it still figures prominently in the assessments and terrain use (and avoidance) of professionals throughout the region.
Sunday night
Cloudy with increasing snowfall bringing 10-25 cm of new snow, greatest in the north of the region. Moderate to strong southwest winds.
Monday
Cloudy with easing but convective flurries bringing 5-10 cm of new snow, again greatest in the north of the region. Light to moderate southwest winds, easing over the day. Treeline high temperatures around -6.
Tuesday
A mix of sun and cloud with isolated flurries. Light northwest winds. Treeline high temperatures around -7.
Wednesday
A mix of sun and cloud. Light southwest winds. Treeline high temperatures around -7.
More details can be found in the Mountain Weather Forecast.
