Avalanche Forecast
Kootenay Boundary
A slab up to 100 cm in depth is consolidating above buried surface hoar which has recently produced large avalanches. At and below treeline you need to carefully travel with intention to avoid convexities, steep features and rocky outcroppings.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid convexities, steep features and slopes with rocky outcroppings.
- It's critical to stay disciplined and choose only well supported, low consequence lines.
- The trees are not a safe haven right now.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Warm temperatures Tuesday likely helped the 20 to 50 cm of recent storm snow to settle and stabilize, but it may still be sensitive to human triggering, especially in steep, convex and/or unsupported features.
Travel and Terrain Advice
- Storm slabs in motion could step down to deeply buried weak layers resulting in large avalanches.
- Caution with wind loaded terrain especially near ridge crests and roll-overs.
Avalanche Summary
On Tuesday reported avalanche activity was limited to minor snowballing and pinwheeling, although a small solar induced slab released from a steep rocky feature late in the day.
On Monday another avalanche failing on the mid-December interface was triggered remotely from 10 m away as a skier approached a rocky outcropping on an east/southeast facing feature around 1900 m, MIN report with photos here. A skier also triggered a small storm slab on a west facing feature around 2200 m Monday which was suspected to have failed on the late December surface hoar.
On Sunday a skier was involved in an avalanche on an east facing treeline feature at Kootenay Pass. A recent crown profile has shown that this avalanche failed on the late November crust/facet interface.
On Saturday we received two reports of large avalanches failing on the mid-December interface. The first was initiated by explosive control work, the size 2.5 avalanche ran on a 35 to 40 degree slope that was southeast through southwest facing at treeline. The second avalanche was a size 3.0 that released naturally on a 30 degree east facing slope between 1900 and 1400 m. This crown was up to 75 cm in depth.
Snowpack Summary
Last week two successive storms produced 25 to 50 cm of low density storm snow that was accompanied by moderate to strong winds out of the east, southeast, south and southwest. The new snow overlies the late December surface hoar which is 3 to 5 mm in size. We don't know much about the distribution of this weak layer yet. Warming alpine temperatures on Tuesday began to moisten the snow surface on steep southerly aspects. Surface hoar has started to blossom on the surface recently too.
Between 60 and 100 cm below the surface you'll find the December 15th interface which consists of a melt-freeze crust on steep, solar, higher elevation slopes and well-developed surface hoar which seems most pronounced in sheltered terrain at and below treeline. The overlying slab is now deep and is gaining cohesion. This interface has hit the tipping point for human triggering as evidenced by recent avalanche activity listed above.
Two laminated crusts created by twin rain events in late November lay just below the December 15th interface, 60 to 100 cm below the surface. There may be facets above the uppermost crust and sandwiched between the two crusts.
Weather Forecast
The weather pattern is developing a change, but a slow change. The cold arctic ridge is beginning to weaken. As the change occurs and the ridge shifts east, a trough pattern at the west coast begins to bring cloud and precipitation to the province, and the icy grip will loosen its hold. The change begins at the Coast on Thursday and over the weekend in the Interior.
THURSDAY: Scattered cloud cover, freezing level at valley bottom, potential for a very light temperature inversion with a pocket of warmer air around 2000 m, light southwest wind, no snow expected.
FRIDAY: Overcast, freezing level around 500 m, light to moderate southwest wind, trace of precipitation possible.
SATURDAY: Overcast, freezing level around 500 m, light to moderate west/southwest wind, 2 to 5 cm of snow possible.
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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 treeline, but it is present below treeline too.