Avalanche Forecast
South Columbia
Previously cold snow below treeline will begin to warm Tuesday which may increase the likelihood of human triggered avalanches. Avoid steep open features, convexities and terrain traps at low elevation as temperatures warm in the afternoon.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Numerous large avalanches have run on these layers in well supported, treed terrain.
- Conservative terrain selection remains prudent in this time of change.
Avalanche Summary
On Sunday there was a widespread natural avalanche cycle to size 3.5. These very large avalanches were running on southwest, south and southeast facing alpine features and were triggered by a combination of above freezing alpine temperatures and direct solar input. Three size 2.5 avalanches likely failing on the early January interface were reported to have ran naturally on a southwest facing slope from 1900 m down to 450 m, covering a snowmobile access road south of Revelstoke. Another remotely triggered size 2.0 avalanche was reported on a northeast facing feature at 2050 m that failed on the early January weak layer.
On Saturday natural avalanches to size 3 were reported from a wide variety of aspects and elevations. Some of the more notable occurrences were cornice failures on north and east facing aspects at upper elevations. Also of note was a size 2.5 avalanche that was remote triggered by a skier on a south/southeast facing feature around 2000 m, likely running on the early January weak layer.
Snowpack Summary
A thin breakable crust has formed on the surface in many locations and fresh surface hoar has been reported too.
The last series of storms left 50 to 70 cm of snow in their wake. Moderate to strong southwest winds previously formed wind slabs in upper elevation terrain.
This snowpack is currently quite complex; there are four Persistent Weak Layers (PWL) that we are monitoring.
The first PWL is known as the early January interface, it is 30 to 90 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects. It is thought to be widespread at all elevations bands and has produced numerous recent large avalanches.
Another surface hoar layer from late December is just below the early January interface.
The next PWL is the mid-December facet/surface hoar/crust combination that is now buried 70 to 150 cm deep and is most problematic at and below treeline. This interface is not thought to be present in the alpine.
The most deeply buried PWL is the late November rain crust. It is found 125 to 200 cm below the surface and has gone dormant for the time being.
Weather Forecast
The ridge that setup the recent inversion will shift east as an offshore front makes landfall with the south coast Tuesday morning. The interior ranges will remain mostly dry with only some light precipitation on Tuesday. A stronger Pacific storm will hit the south coast on Wednesday morning with precipitation spilling into the interior on Wednesday afternoon. Light snowfall is expected to continue through Thursday.
TUESDAY: Increasing cloud cover, freezing level initially at valley bottom rising to around 1000 m in the afternoon. Moderate southwest wind, 2 to 10 cm of snow in the afternoon, trace of snow possible Tuesday night.
WEDNESDAY: Increasing cloud cover throughout the day, freezing level beginning around 500 m rising to about 1800 m in the late afternoon, moderate southwest wind, 3 to 10 cm of snow possible.
THURSDAY: Overcast, freezing level beginning around 1700 m lowering to 1400 m throughout the day, moderate southwest wind, 3 to 12 cm of snow possible.
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Alpine temperatures are expected to remain warm Monday night and above freezing temperatures are expected between valley bottom and 1000 m Tuesday, which may increase the likelihood of human triggered avalanches in unusual locations at low elevation.