Wind Slabs
N
NE
E
SE
S
SW
W
NW
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2
Pockets of soft wind slab may be found in leeward features in the alpine. The underlying crust offers a slick bed surface for avalanches.
Avalanche forecast
View on mapSouth Coast Inland
Dec 14 – 15, 2020Avalanche Canada
Archived · expired 6 years ago
Avalanche danger
Wed
Thu
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
Highlights
Watch for wind loaded pockets of snow especially around ridge crests and roll-overs in the alpine.
Avalanche problems
Deep Persistent Slabs
NNEESESSWWNW- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 1.5–2.5
In the north of the region, a crust/facet layer sits near the base of the snowpack. It is surrounded by weak crystals and produces hard results in snowpack tests. In shallow, rocky areas in the alpine, it may remain at a depth triggerable by humans. On December 1, a natural cornice fall triggered a size 3 avalanche on this layer proving it is triggerable by large loads.
This layer is not a problem in the south of the region.
Confidence
Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.
Weather Forecast
Sunday night: Trace of new snow, light northwest ridgetop wind, freezing level valley bottom.
Monday: Localized flurries, around 8cm near Hope, light southwest ridgetop wind, alpine high -6 C, freezing level 500 m.
Tuesday: Up to 10 cm new snow, strong southwest ridgetop wind, alpine high -5 C, freezing level 800 m.
Wednesday: Up to 5 cm new snow, strong southwest ridgetop wind, alpine high -4 C, freezing level 800 m.
Avalanche Summary
As the wind picks up, we can expect to see natural and human triggered wind slabs in lee features at upper elevations.
On Saturday, small loose wet avalanches were observed on solar aspects around treeline.
On Tuesday December 1, a large size 3 natural avalanche was observed on a NE aspect at 2400 m in the Duffy area. It was reported as a cornice failure triggering the slope below and appeared to have slid on the early November crust near the base of the snowpack.
Have you been out and about in the mountains? If so please submit your observations to the Mountain Information Network (MIN). It doesn't have to be technical - photos are especially helpful! Thank you so much for all the great MINs submitted so far!
Snowpack Summary
- In the north, moderate southwest wind is redistributing up to 35 cm of dry alpine snow into wind slabs sitting over a thin zipper crust above 2300 m. As you go down in elevation, the surface snow gets thinner and the crust gets thicker. Between 1600 and 2000 m, the crust is punchy and unsupportive. In the lower snowpack, a crust/facet layer sits near the ground. The most recent avalanche observed on this layer was on December 1st, while recent snowpack tests in the Cayoosh zone found this layer down 60 cm and unreactive. We have a lot of uncertainty on the reactivity of this layer so we're keeping it on our radar.
- In the south, a surface melt-freeze crust exists on solar aspects. In the alpine, moderate southwest wind is redistributing around 20 cm of dry snow into wind slabs over the rain crust. This crust is 10-20 cm thick, reaches all the way to mountaintop and seems to be bonding well to overlying snow. Below, the snowpack is moist and dense.
Terrain and Travel
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Wind slabs are most reactive during their formation.
- A crust on the surface will help bind the snow together, but may make for tough travel conditions.