Start small and gather information about the depth and slab properties of new snow as you move into the terrain. Conditions at higher elevations will likely be a step more reactive, so keep overhead hazards in mind as you plan your line.
Read more about managing our current deep persistent slab problem in our latest Forecasters' Blog.
In higher snowfall parts of the region, deep accumulations of new snow that haven't formed into a slab are likely to continue producing large sluffs with rider traffic on steep slopes.
Continuing snowfall is loading a couple of storm interfaces about 30 cm and 70 cm deep. Although we expect surface instabilities to gradually become limited to wind-loaded areas, al steep terrain should be approached with serious caution over the near term. Surface storm or wind slabs in motion may also entrain accumulations from the last storm to create larger, more destructive avalanches.
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.
We don't have fresh observations from Thursday's storm yet, but observations from operators in the region observing up to 25% of their tenures after the weekend storm generally show no new avalanches. Reports closer to the immediate aftermath of the storm described numerous small dry loose avalanches and several storm slabs releasing with skier traffic and ski cutting, generally below treeline and limited to size 1 or smaller.
We expect some degree of a natural avalanche cycle also took place during the weekend storm at higher, wind affected elevations, especially in areas that were on the higher end of our new snow totals. This MIN report from Westridge gives a good indication of conditions that were likely fairly widespread in the region - perhaps similar to what we'll see for Thursday's observations as well.
A few very large (size 3.5 to 4) deep persistent slab avalanches were also observed over last week, which likely occurred during the very windy arctic outflow event.
Looking forward, we expect a mix of gradually diminishing storm slab reactivity, a shift toward wind slabs being the most reactive slab problem, and continued dry loose hazard in sheltered areas where snow remains low density.
Another round of stormy weather mid-week has so far brought about 15-30 cm of new snow to the region, with more to come overnight Thursday. For the most part the latest snow adds to 20-50 cm of low density storm snow from the weekend, but it may also have buried recent wind slabs in more exposed areas and likely a thin sun crust on sun-exposed aspects.
The interface below the snow from the weekend storm includes small surface hoar in lower elevation sheltered areas and more widespread faceted (sugary) snow and heavy wind effect. Now roughly 30-60 cm deep, this interface remains in question with storm slabs having been generally slow to form over it in recent days.
Another small layer of surface hoar crystals may be found about 80 to 150 cm deep, particularly in areas sheltered from the wind around treeline. This layer had been gaining strength prior to the last storm and is currently considered dormant. We are still light on observations showing whether it did or didn't wake up in isolated areas from the weight of the recent 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.
Thursday night
Cloudy with continuing convective flurries bringing another trace to 5 cm of new snow. Moderate to strong southwest winds.
Friday
Cloudy with easing convective flurries bringing up to 5 cm of new snow and storm totals to 20-40 cm. Moderate southwest winds, easing over the day. Treeline high temperatures around -10.
Saturday
A mix of sun and cloud. Light east winds. Treeline high temperatures around -8.
Sunday
Mainly cloudy. Light northeast winds. Treeline high temperatures around -9.
More details can be found in the Mountain Weather Forecast.
