Fresh, reactive wind slabs likely exist at upper elevations. Riders may seek more sheltered areas around treeline to avoid these wind slabs but should consider that this is where the persistent slab problem may be lurking. It's a good time to keep your terrain choices conservative.
Strong westerly winds combined with new snow will likely form fresh and reactive wind slabs in the alpine and open areas at treeline.
Small avalanches in the upper snowpack could trigger deeper weak layers, creating a larger than expected avalanche.
Buried layers of surface hoar and facets have been reactive to human triggers in recent days. Reactivity has been observed in sheltered areas at treeline, where the surface hoar may be preserved, and in wind-loaded areas at upper elevations, where a cohesive slab has been formed above.
Observations on this layer are limited. In times of uncertainty such as this, our best defense is to keep terrain choices conservative and reduce your exposure to avalanche terrain where possible.
On Monday, explosive testing targeted the persistent slab problem with no results, however, skier-controlled wind slabs were initiated up to size 1 as well as explosive-controlled wind slabs size 1.5.
On Sunday, a MIN report from Tunnel Creek reported reactivity in a snowpack test on the Mid-November layer on a south aspect. In this area, the layer is presented as facets on a crust. They also observed a large natural avalanche on a west-facing slope at treeline.
I suspect wind slabs will be present and reactive on Wednesday as well as loose dry avalanches (sluffing) within the recently fallen low-density surface snow, especially from steep slopes and terrain features.
Up to 15 cm of low density, new snow fell overnight Tuesday and Wednesday. This new snow will add to the ~25 cm of storm snow that fell early in the weekend. In wind-affected terrain, westerly winds are expected to redistribute this new snow into fresh wind slabs. In sheltered terrain, cold temperatures will likely maintain low-density, powdery snow.
The middle of the snowpack consists of weak sugary layers of facets and surface hoar. A widespread rain crust remains near the ground at treeline and below treeline.
At treeline, snowpack depths vary from 120-200 cm.
Tuesday Night
Cloudy with light snowfall amounts 2 to 5 cm. Westerly winds 40-70 km/h at ridgetop. Treeline temperatures drop to -13 C.
Wednesday
Cloudy with possible sunny breaks, generally 5 cm accumulation. Moderate to strong westerly winds at ridgetop. Temperatures reach a high of -10 C.
ThursdayCloudy with snow forecast later in the day and overnight, with possible accumulations 10-15 cm. Strong southwest winds at ridgetop. Average temperature near -8 C.
FridayCloudy with snowfall, up to 5 cm of accumulation. Gusty wind from the west/ southwest at ridgetop. Treeline temperatures reach a high of -6 C and a low of -10 C.
More details can be found in the Mountain Weather Forecast.
