A problematic weak layer has been producing large, hair-triggered avalanches. Careful snowpack evaluation, cautious route-finding and conservative decision-making are critical.
Watch for pockets of fresh wind slab in atypical terrain features. This pattern is most likely to be found at elevations with soft snow available for transport by outflows.
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 to very large (size 2-4) natural and remotely-triggered persistent slab avalanches have been reported in recent days. Slabs have shown propagation as wide as 1 km and remote triggers as far away as 1km!
A couple of MIN reports from South Douglas on the weekend paint the picture: 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.
Extensively wind-affected surfaces exist in the alpine. Soft snow at lower elevations will likely be redistributed as outflow winds pick up this week. 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.
Tuesday night
Partly cloudy. 10 to 30 km/h east outflow winds. Treeline temperature -12 to -16 °C.
Wednesday
Sunny. 20 to 40 km/h east outflow winds. Treeline temperature -12 to -16 °C.
Thursday
A mix of sun and cloud with isolated flurries bringing up to 5 cm. 40 to 60 km/h east outflow winds. Treeline temperature -13 to -17 °C.
Friday
A mix of sun and cloud with isolated flurries bringing up to 5 cm. 20 to 40 km/h east outflow winds. Treeline temperature -10 to -14 °C.
More details can be found in the Mountain Weather Forecast.
