Avalanche Forecast
Sea To Sky
Danger will gradually increase as new snow accumulates. The persistent slab problem warrants conservative terrain choices at treeline and below treeline elevations.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Minimize exposure during periods of heavy loading from new snow and wind.
- Use conservative route selection and choose moderate angled terrain while travelling at treeline elevations.
- Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Fresh wind slabs will build throughout the day at higher elevations.
Travel and Terrain Advice
- Be cautious as you transition into wind affected terrain.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Avalanche Problem 3: Cornices
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Cornices are inherently unstable, unpredictable, and demand respect. New snow and warming will likely make cornices extra brittle.
Travel and Terrain Advice
- Firm cornices may pull back into flat terrain at ridgetop if they fail.
- Give cornices a wide berth when traveling on or below ridges.
Avalanche Summary
Persistent slab activity continued on Tuesday. A small wind slab on a northwest aspect in the McBride Range stepped down and triggered a much larger persistent slab avalanche when it reached 1900 m. The result was a size 3 avalanche (100 cm thick) that propagated across the entire bowl and ran all the way to the bottom of the valley. A few smaller size 1 natural slabs were also observed at and below treeline.
Several persistent slab avalanches were reported last weekend, including a size 3 avalanche that was remotely triggered on a west aspect at 1900 m in the Blackcomb backcountry and presumably failed on a buried surface hoar layer (see photo and details here). At a similar elevation, a size 2 avalanche failed in a north-facing chute and triggered additional smaller avalanches on nearby slopes. Closer to Squamish, a natural size 2 avalanche failed on a south aspect at 1750 m (see photo and details here). These avalanches highlight a persistent slab problem that exists on all aspects around treeline elevations.
Snowpack Summary
New snow will accumulate on Thursday and Friday and form extra deep deposits in wind loaded terrain. The new snow is falling on a sun crust on steep south-facing slopes, cold dry snow on polar aspects, and wind affected snow at upper elevations.
Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden reactive results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface.
Variable winds in the past month have produced cornices on many ridgelines. They will become touchier as they grow in size, as temperatures rise, and when they are subject to the strong late-winter sun on clear days.
Weather Forecast
THURSDAY: Flurries increasing throughout the day with 5-15 cm of snow possible by the afternoon, moderate to strong southwest wind, freezing level rising to around 1400 m.
FRIDAY: Another 5-15 cm of snow overnight and then clearing in the afternoon, light wind, freezing level dropping to around 800 m.
SATURDAY: Mostly sunny, moderate south wind, freezing level rising to around 1500 m.
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A layer of surface hoar, sugary facets, and/or crust is buried 50-100 cm deep and has produced widespread whumpfing, concerning snowpack test results, and a few large remotely triggered avalanches. Upper treeline elevations are the greatest concern.