Take a conservative approach in the wake of the storm. Storm slabs are primed for human triggering.
We have uncertainty as to whether a layer of surface hoar buried 100-150 cm deep remains a problem after a widespread natural storm slab avalanche cycle on Tuesday may have triggered it in areas where it posed a problem.
30-50 cm of new snow fell at upper elevations with strong wind on Tuesday. Storm slabs will be primed for human triggering Wednesday.
Tuesday night: Snowfall 5-15 cm. Moderate southwest wind. Alpine low around -8 °C. Freezing level dropping to 500 m.
Wednesday: Flurries around 5 cm. Moderate southwest wind. Alpine high around -6 °C. Freezing level 1000 m.
Thursday: A mix of sun and cloud. Moderate southeast wind. Alpine high around -5 °C. Freezing level 1200 m.
Friday: A mix of sun and cloud. Moderate south wind. Alpine high around -5 °C. Freezing level 1200 m.
Observations during the storm have been limited by visibility. Preliminary reports include size 1-2 loose wet avalanches observed near valley bottom. We expect a large, widespread storm slab avalanche cycle to have occurred, including step-downs to the persistent layer.
Prior to the storm, reports of persistent slab avalanches were steadily coming in over the last week from northwest of Terrace. These avalanches were large to very large (size 2-3), failing on a weak layer buried 60-100 cm deep mostly on northeast facing slopes. These avalanches were easily triggered by riders and vehicles, some remotely or sympathetically, and propagating long distances.
30-50 cm of heavy new snow has been distributed by strong southwest wind at upper elevations. Below 1500 m, new snow depths taper and the snow may sit over a wet or crusty upper snowpack.
A weak layer of surface hoar is now buried 100-150 cm deep. A thick rain crust from mid-February 130-200 cm deep caps a well consolidated lower snowpack.
