Avalanche Forecast
South Columbia
Avalanche danger will increase as new snow and wind load the snowpack. Recent storms have been very effective at triggering deeply buried weak layers and a similar pattern is expected in the coming days.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Uncertainty is best managed through conservative terrain choices at this time.
- Anticipate avalanches running full path when managing overhead hazards.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
New snow and strong west winds are expected to build fresh storm slabs over the day on Friday. Snowfall amounts are uncertain, but snow stability will be on a decreasing trend throughout the day.
Travel and Terrain Advice
- Watch for the first touchy slabs to form in the lee of ridges and exposed terrain features.
- Storm slabs may step down to deeply buried weak layers to produce very large avalanches.
Avalanche Summary
Reports from the north of the region on Wednesday included an observation of a Size 2.5 wind slab triggering remotely from 300 metres away on a low angle slope at 2300 metres. Elsewhere, storm slabs were observed running naturally and with explosives from Size 1.5-3. South aspects were especially active where solar warming served as a trigger.
Explosives control in the adjacent North Columbias yielded numerous persistent Slab results from Size 2-3.5 on all aspects at all elevations. The deep mid-December layer and an even deeper layer from November were both frequent failure planes. The mid December layer is also suspected in two natural Size 4 releases in and near the Glacier National Park area.
On Wednesday a Size 2 natural avalanche struck a ski touring group on a northeast facing avalanche path outside of Revelstoke, more details available here.
On Tuesday natural avalanche activity was widespread, running on all aspects and elevations. Storm and wind slabs were reported to Size 3, persistent slab avalanches failing on the mid-December interface ran as large as to Size 4. Large avalanches were running even at low elevations. See here for a good example in a MIN report.
Snowpack Summary
60 to 110 cm of snow fell between Sunday and Tuesday night. On Monday temperatures warmed up to -1 C at tree line. Winds were strong to extreme from the south, building cornices and creating wind slabs on leeward slopes.
The new snow sits on a complex snowpack and there are three active weak layers that professionals are monitoring:
1) 70 to 110 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at tree line elevations and possibly higher. This has been the most active failure plane for recent large avalanches in the Columbias.
2) Deeper in the snowpack, the early-January persistent weak layer is 100 to 140 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands.
3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 120 to 170 cm deep. It is most problematic at and below tree line.
Weather Forecast
Friday: Cloudy with flurries bringing 10-20 cm of new snow, increasing overnight. Moderate to strong west winds, continuing overnight. Freezing level rising to 1500 metres with alpine high temperatures around -4.
Saturday: Cloudy with continuing flurries bringing another 5-10 cm of new snow. Strong northwest winds easing over the day. Freezing level to 1400 metres with alpine high temperatures around -5.
Sunday: Cloudy with flurries bringing 10-20 cm of new snow over the day. Light variable winds. Freezing level near valley bottom, rising over the day. Alpine high temperatures around -7.
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Several deep weak layers in the snowpack remain sensitive to heavy triggers. The coming storm pattern is likely to produce more avalanches that step down to these layers. Seek out simple terrain that doesn't expose you to large avalanche paths.