A problematic weak layer has been producing large, hair-triggered avalanches. Careful snowpack evaluation, cautious route-finding and conservative decision-making are critical.
Pockets of wind slab may remain triggerable in leeward terrain features. The main concern for these surface avalanches is their potential to step down to buried weak layers, resulting in large avalanches.
Large slab avalanches have been easily triggered on weak grains over a buried crust. This weak layer has shown wide propagation across large terrain features.
Large (size 2-3) natural and remotely-triggered persistent slab avalanches have been reported in recent days. These avalanches have been failing on weak grains over a crust. A couple of MIN reports from South Douglas on Friday demonstrate the wide propagations and large trigger distances we've seen. This sobering near miss surprised riders as a fracture line wrapped around a feature and this MIN describes skiers triggering large avalanches from valley bottom 1 km away.
Extensively wind-affected surfaces exist in the alpine. Soft snow can be found in sheltered and lower elevation terrain. Below 1000 m, surface snow is moist and/or crusty.
50 to 100 cm of snow sits over a significant weak layer. The layer involves weak grains of surface hoar and facets sitting over a crust. This layer has been the failure plane for recent large avalanches with wide propagation.
The remainder of the snowpack is well settled and bonded. Treeline snow depths are around 160 cm.
Monday night
Mostly cloudy. Isolated flurries with minimal accumulations. 10 to 20 km/h variable ridgetop wind. Treeline temperature -5 °C.
Tuesday
Mostly cloudy. Isolated flurries with minimal accumulations. 10 to 30 km/h east outflow winds. Treeline high temperature -8 °C.
Wednesday
Mostly sunny north of Stewart. Isolated flurries with minimal accumulations near Terrace. 20 to 40 km/h east outflow winds. Treeline high temperature -12 °C.
Thursday
A mix of sun and cloud with isolated flurries bringing up to 5 cm. 30 to 50 km/h southeast outflow winds. Treeline high temperature -14 °C.
More details can be found in the Mountain Weather Forecast.
