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Avalanche Forecast

Archived

Feb 15th, 2022–Feb 16th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Columbia.

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.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A passing frontal system will bring light snowfall, with greater amounts forecast for Thursday.

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: Snowing 10-20 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 an isolated wind slab up to size 1.5 was reported as well as a natural cornice fall. These events did not pull deeper slabs on the slopes below. 

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 recreationists 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. 

Snowpack Summary

A light amount of snow is expected to bond poorly to the old snow 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 40 to 100 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.
  • 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.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.