Avalanche Forecast

A storm system brings snowfall to the region Sunday night which may linger through the early part of the day on Monday. Modelled snowfall amounts and timing are highly variable which is creating a lot of uncertainty for conditions on Monday. 

Sunday Night: Snowfall 10-20 cm, moderate SW wind, treeline temperature around -6 C°.

Monday: Snowfall up to 5 cm in the morning, sunny breaks in the afternoon, light to moderate W-NW wind, treeline high around -4 C°.

Tuesday: A mix of sun and cloud, light NW wind, treeline high around -6 C°.

Wednesday: Mainly sunny, light variable wind, treeline high around -10 C°.

On Saturday, a skier triggered a size 1.5 wind slab on an E aspect in the alpine which failed down 5-20 cm. On Friday, explosives triggered a size 1 slab on a north aspect near treeline which failed on a reloaded bed surface of the early December interface. A skier and explosives also triggered a couple wind slabs in very steep terrain and explosives triggered a cornice which scrubbed a gully down to the ground. Some solar triggered loose avalanches were also reported on steep rocky slopes. 

Avalanche activity on the early-December weak layer described in the snowpack summary has been sporadic over the past few weeks. Prior to this most recent drought, we were tending to see reports of avalanches on this layer every few days. Most of the avalanches occurred at elevations around 2000 m. Possible natural triggers include daytime warming, warming from the sun, cornice falls, or smaller avalanches stepping down. Human triggering is most likely in steep, rocky slopes with a shallow or thin-to-thick snowpack.

The new snow is burying a highly variable snow surface which consists of wind affected surfaces in exposed high elevation terrain, a melt freeze crust at lower elevations and on solar aspects extending into the alpine, and/or widespread surface hoar in sheltered areas which is appears to typically be 5-15 mm. 

Some older thin surface hoar layers are 20-40 cm deep, but have not been producing concerning results in recent snowpack tests. 

The most notable layer of concern in the snowpack is a facet/crust layer that formed in early December and ranges in depth between 70 cm along the shallower eastern Purcells and up to 150 cm in the western Purcells. This recent blog post goes into more details on this interface and why it is expected to continue to create problems for the rest of the season. 

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
• Conditions may have improved, but be mindful that deep instabilities are still present.