Avalanche Forecast
Kootenay Boundary
15 to 25 cm of snow Monday night with significant southwest wind will add to the storm slab that rests on the early January interface and may overload more deeply buried weak layers in our complex snowpack. Keep terrain choices conservative.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use caution at and above treeline, wind stiffened storm slabs are expected to be widespread.
- Choose conservative lines and watch for clues of instability.
- Storm slabs in motion may step down to deeper weak layers resulting in large destructive avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Surface hoar is now buried up to 100 cm deep and has recently produced large human triggered avalanches. This slab appears to be most sensitive at tree line, but it is present below tree line too.
Travel and Terrain Advice
- Any steep opening in the trees should be treated as suspect right now.
- It's critical to stay disciplined and choose only well supported, low consequence lines.
- Avoid convexities, steep features and slopes with rocky outcroppings.
Avalanche Summary
On Monday control work produced avalanches to size 2.0 on northwest through east facing slopes. Both natural and skier triggered loose dry avalanches to size 1.5 were also reported.
On Sunday a small skier triggered avalanche was reported on a southeast facing feature at 1600 m. Although only a size 1.0, this avalanche had a crown height of 55 cm and failed on the mid-December surface hoar. A second skier triggered avalanche on a north facing feature had a crown depth of 40 cm.
Last Thursday a skier triggered a size 3.0 avalanche just after entering the east face of Evening Ridge at 2000 m near Nelson. The avalanche released to ground and the late November crust was likely involved. The avalanche caught and carried the skier for over 300 m, resulting in significant injuries. Subsequent avalanche control in the area produced two additional size 2.5 avalanches.
On New Years Eve a size 3 avalanche on an east facing treeline feature at Kootenay Pass resulted in a single fatality. A crown profile has shown that this avalanche failed on the late November crust. Click here to see the Mountain Information Network report for this incident.
Snowpack Summary
10 to 25 cm of new snow now sits on a crust on steep southerly aspects and/or a newly formed layer of surface hoar that was buried January 5th. A series of storms last week produced 25 to 50 cm of low density snow. This means that a surface hoar layer buried late in December is now 40 to 50 cm deep. Dig a bit deeper, you may find yet another surface hoar layer between 60 and 110 cm below the surface. This layer was buried mid-December and is most pronounced at treeline, but is present below treeline also. The overlying slab is now deep and is gaining cohesion with time and continued warm temperatures, as evidenced by recent avalanche activity listed above.
Two laminated crusts created by twin rain events in late November lay just below the mid-December interface, 70 to 110 cm below the surface. Facets may be found sandwiched between the two crusts and have been observed above the uppermost crust too. In shallow rocky terrain the mid-December surface hoar and the late November crust seem to be reacting together which is a volatile combination.
Weather Forecast
Continued snowfall is expected through Tuesday before a brief lull in the action Wednesday. Thursday's system may be pretty juicy, stay tuned for details.
MONDAY NIGHT: Freezing level at valley bottom, moderate to strong southwest wind, 15 to 25 cm of snow expected.
TUESDAY: Overcast, freezing level around 1400 m, light southwest wind, 5 to 10 cm of snow expected.
WEDNESDAY: Overcast, freezing level at valley bottom, light southwest wind, 1 to 5 cm of snow possible.
THURSDAY: Overcast, freezing level at valley bottom, moderate south wind, 10 to 20 cm of snow possible.
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15 to 25 cm of snow Monday night accompanied by significant southwest wind is expected to add to the slab that rests on the early January interface. Both natural and human triggered avalanches are likely as the upper snowpack adjusts to the new load.