Avalanche Forecast

SATURDAY NIGHT: Cloudy, no precipitation, moderate northwest wind, treeline temperatures around -3 C, freezing level lowering to valley bottom.

SUNDAY: Cloudy skies, no precipitation, westerly wind increasing moderate by midday, treeline temperatures around -4 C, possible temperature inversion with alpine temperatures of -1, freezing level rising to 1000 m.

MONDAY: Flurries, moderate southwest wind, treeline temperatures around -5 C, possible temperature inversion with alpine temperatures of -1, freezing level around 1000 m.

TUESDAY: Snow 5-10 cm, light northwest wind, treeline temperatures around -6 C, freezing level rising to 500 m.

No new avalanches were reported in the last 24h.

Thursday, large avalanches (size 2.5) with impressive propagation were triggered by strong solar radiation and warm temperatures (+5 C at treeline). Several loose wet avalanches were also observed at lower elevations along with significant pinwheeling. While in motion, some of these loose avalanches pulled large storm slabs, scouring avalanche paths to the ground in places.

Wednesday, a widespread avalanche cycle occurred, with numerous sizes 1-2 storm slabs avalanches and one size 3 avalanche on Ymir Mountain. These avalanches were 20-40 cm thick, and in many cases were suspected to have failed on a recently buried surface hoar layer (see photos in the MIN post). 

We have not heard reports of persistent slab avalanches since last weekend, when we saw numerous sizes 2 to 3 avalanches releasing on the early December facet/crust layer. Prior to these avalanches, we were seeing a regular pattern of large destructive avalanches on this layer at the start of the month. These avalanches mostly occurred on thin, wind-affected slopes near ridge tops. 

Winds have redistributed the dry alpine snow on lee slopes and open areas at treeline. Around 1900 m and below, a crust is now capping the dense 10-30 cm of recent snow which is continuing to settle with the mild temperatures. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Below the recent snow, a layer of feathery surface hoar and melt-freeze crusts are found, which seems to be still reactive in isolated areas. Lower elevations have gone through a melt-freeze cycle and snow is still from warming/rain event. 

The early December crust/facet layer has been responsible for sporadic but very large, persistent slab avalanches over the past month. The crust is now buried 120-200 cm deep except in thin, wind-affected areas near ridgetops where most of the recent avalanches have been triggered.

• Keep in mind that human triggering potential persists as natural avalanching tapers off.
• Be alert to conditions that change with elevation and wind exposure.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.