Avalanche Forecast
Issued: Feb 15th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
swerner,
Avalanche Canada
New snow may bond poorly to the underlying crust. Small but reactive pockets of wind slab may form in lee areas in the alpine and treeline.
Manage open slopes at treeline carefully where triggering a persistent slab avalanche is most likely if a surface crust is not present.
Summary
Confidence
Weather Forecast
A more unsettled weather pattern will bring a mix of sun and cloud and light snowfall throughout the week.
Tuesday Overnight: Mainly cloudy, light snowfall 5-10 cm. Freezing level dropping to valley bottom. Light to moderate northwesterly winds.
Wednesday: Partially cloudy with light flurries. Freezing level rising to 1000 m. Moderate northwesterly winds.
Thursday: Mainly cloudy and snowing with 5-10 cm forecast. Freezing level rising to 1500 m in the afternoon. Moderate to strong northwesterly winds.
Friday: Light snow 5 cm. Freezing level rising to 1500m. Strong to extreme westerly winds.
Avalanche Summary
If you see more than 10 cm of fresh snow expect to see some isolated pockets of reactive wind slab on leeward slopes and terrain features on Wednesday.
On Monday a few persistent slab avalanches were reported up to size 3 from various aspects 1900 m to 2300 m. These slabs looked to be 24 hours old.
Last weekend, natural and artificially triggered persistent slabs were reported at treeline and above from solar aspects.
Last week, near-daily reports came in of human-triggered persistent slab avalanches on the January 30th weak layer, with the associated surface hoar layer taking both recreationalists and professionals by surprise. Reactivity has begun to taper but this buried weak layer should not be taken lightly as it may now present a low-probability, high-consequence problem. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks and on steep convexities. Check out this recent MIN report from the south of the region where the surface hoar is very prominent and shows propagating results in an extended column test.
Snowpack Summary
A light amount of new snow is expected to bond poorly to the old surface. This surface is comprised of near-surface faceting and in some areas, surface hoar growth overlying a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. North aspects may still hold soft "ish" snow down to 1500 m.
Several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of buried surface hoar. This surface hoar has been the dominating feature in the past few weeks. It was buried in late January and exists 30 to 80 cm deep in the snowpack. The surface hoar is most prominent in sheltered openings at and below treeline.
The facet/crust layer that formed in early December is now buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Surface hoar distribution is highly variable. Avoid generalizing your observations.
Problems
Wind Slabs
New snow may be redistributed by northwest winds to create small but reactive pockets of wind slab in the alpine and treeline.
Aspects: North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer formed by clear skies in late January may be found 40 to 80 cm deep in the snowpack. This layer consists of facetted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.
This surface hoar layer has been the culprit of several large human-triggered avalanches in the past week and remains a concern, especially in sheltered areas at treeline. Terrain features to be particularly cautious around include the lee side of ridges, openings in trees, cut blocks, and burns. Where a thick, supportive crust is present on the surface, avalanches on this layer are unlikely. Triggering this layer from a distance away is a concern, watch out for adjacent and overhead slopes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 16th, 2022 4:00PM
