Extensive reports of powerful sluffing and touchy storm slabs have resulted from the storm, even with very limited observations. Stick to low consequence terrain while the new snow settles and put your guard way up if the sun pokes out on Tuesday.
In higher snowfall parts of the region, deep accumulations of new snow that haven't formed into a slab are likely to create large sluffs with rider traffic in steep areas.
With up to about 50 cm of new snow from the weekend overlying weak grains like faceted snow and small surface hoar, we may see storm slab reactivity persist a bit longer than usual.
What's more certain is that large wind-loaded slabs perched on leeward (north-facing) terrain will be primed for human triggering.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's deep burial depth, but storm slab avalanches in motion have the potential to step down. Suspect terrain for human triggering includes steep, thin, shallow, and rocky terrain, which is often found near ridgelines.
Very limited observations from the weekend storm showed small dry loose avalanches releasing with skier traffic below treeline. We also expect some degree of a natural avalanche cycle took place at higher, wind affected elevations, especially in areas that were on the higher end of our new snow totals. This MIN report from Westridge is definitely in line with the conditions we expect to persist through Tuesday.
Many small to large (size 1 to 2.5) wind slabs were triggered naturally and by riders over the past few days. They mostly occurred on south to west aspects at alpine elevations resulting from northeasterly outflow winds. A few very large (size 3.5 to 4) deep persistent slab avalanches were also observed over the week, which likely occurred during very windy conditions.
Looking forward, storm slabs from the weekend may remain sensitive to human triggering a bit longer than usual, owing to the weak faceted snow they overlie. Otherwise we expect surface instabilities to gradually become more focused toward wind loaded areas.
Stormy conditions over the weekend brought up to about 50 cm of new snow to the region along with strong southwest wind on Saturday. The new snow buried an interface which includes reports of faceted (sugary) surface snow, small surface hoar in lower elevation sheltered areas, and more widespread heavy wind effect and wind slabs at higher elevations from recent northeast winds.
Prior to the storm, a small layer of surface hoar crystals could be found about 50 to 100 cm deep, particularly in areas sheltered from the wind around treeline. This layer appears to be gaining strength and is currently considered dormant, but could have woken up in isolated areas from the weight of the new snow.
Large and weak facets that formed in November are found near the base of the snowpack. Although the likelihood of triggering this layer is low at this time, the consequence of doing so remains very high. This layer is most likely to be human-triggered in thin, rocky slopes at alpine and upper treeline elevations.
Monday night
Mainly cloudy with isolated flurries. Light east winds.
Tuesday
Mainly cloudy with isolated flurries. Light east winds becoming variable. Treeline high temperatures around -9 °C.
Wednesday
Cloudy with isolated flurries, increasing in late afternoon and overnight. Winds increasing to Moderate southwest by end of day. Treeline high temperatures around -10.
Thursday
Cloudywith continuing snowfall bringing 10-15 cm of new snow, including overnight amounts. Strong southwest winds easing a bit over the day. Treeline high temperatures around -8.
More details can be found in the Mountain Weather Forecast.
