New snow and wind are creating very dangerous avalanche conditions. Travel in avalanche terrain is not recommended.
A buried weak layer is being rapidly loaded by the new snow. Slabs failing at this depth will result in large and destructive avalanches.
New snow and strong west winds are building reactive storm slabs. The highest danger will be on steep, leeward slopes below ridgetops.
Observations have been limited by poor visibility during the storm. On Tuesday, natural storm slabs were observed up to size 3 in the alpine and size 2 below treeline. We expect similar natural avalanche activity to be ongoing through the storm on Thursday.
On Monday, north of Stewart, a vehicle triggered a size 1.5 persistent slab avalanche on a northwest aspect in the alpine.
Another 15-30 cm of snow is expected by the end of the day Thursday, bringing storm totals to 30 to 70 cm. The new snow arrives with strong to extreme winds, particularly near Terrace, so significant wind transport is expected at upper elevations. Below 1200 m, the snow surface may be moist, wet or crusty.
The recent snow isn't expected to bond well where it sits on a layer of buried surface hoar, facets, or a thin crust.
A weak layer of surface hoar and facets overlying a crust is buried 60 to 120 cm deep in the southern parts of the region, and up to 200 cm deep in areas north of Stewart. If the new snow overloads this layer, causing it to fail, the resulting avalanches will be very large and destructive.
Wednesday night
Cloudy with around 5 cm of snow. Southwest ridgetop wind increasing 20 to 50 km/h. Treeline temperature -2°C. Freezing level 1200 m near Terrace, 800 m near Stewart.
Thursday
Cloudy with 15 to 30 cm of snow. 70 to 100 km/h southwest ridgetop wind. Treeline temperature -1 °C. Freezing level 1200 m near Terrace, 800 m near Stewart.
Friday
Cloudy with 10 to 20 cm of snow. 50 to 70 km/h southwest ridgetop wind. Treeline temperature -2 °C. Freezing level 800 to 1000 m.
Saturday
Cloudy. 30 to 40 km/h northwest ridgetop wind. Treeline temperature -5 °C. Freezing level valley bottom.
More details can be found in the Mountain Weather Forecast.
