Avalanche Forecast
Kootenay Boundary
It's getting trickier as the recent storm snow settles into a cohesive slab and the mid-December surface hoar becomes active. With all this uncertainty conservative terrain selection remains prudent.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
- Avoid wind loaded terrain at and above treeline, especially near ridge crests and roll-overs.
- Good day to choose conservative lines and carefully watch for clues of instability.
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 avalanches. Increased settlement and cohesion of the overlying slab will likely make this interface more sensitive to human triggering.
Travel and Terrain Advice
- Avoid steep slopes and convexities at and below treeline where buried surface hoar may be preserved.
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
- Storm slab avalanches in motion could step down and trigger larger persistent slab avalanches.
Avalanche Summary
On Sunday a skier was involved in an avalanche on an east facing treeline feature at Kootenay Pass. Preliminary information puts this incident close to what the guidebook calls Missile Ridge Northeast 2. Further details are not available at this time.
On Saturday we received two reports of what might be the first 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. Control work produced numerous other storm slabs to size 2 on northwest, north, northeast, southeast, south and southwest aspects. Natural avalanches to size 2 were reported on north facing features at 2100 m.
Snowpack Summary
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 3 to 5 mm surface hoar, but we don't know much about the distribution of this weak layer yet.
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 bond at this variable interface is of critical importance, especially in areas where the overlying slab is deep and well-consolidated.
The lower snowpack is thought to be strong and well-settled.
Weather Forecast
The ridge continues to dominate the weather pattern, which means cool dry conditions on Monday. The setup changes slightly on Tuesday as warm air rides up and over the cold air in the valleys producing a pronounced Temperature Inversion.
MONDAY: A few clouds, freezing level at valley bottom, light to moderate northwest wind, no snow expected.
TUESDAY: Temperature Inversion with below freezing air in the valley, above freezing (warmer) air between 2000 m and about 3000 m. Scattered cloud, light northwest wind, no snow expected.
WEDNESDAY: Temperature Inversion with below freezing air in the valley, above freezing (warmer) air between 1800 m and about 2500 m. Mostly clear skies, light northwest wind, no snow expected.
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25 to 50 cm of new snow has fallen in the last few days accompanied by wind mainly out of the south. Human triggered avalanches are becoming more likely as time and wind loading allow the snow to settle into a more cohesive slab.