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Avalanche Forecast

Archived

Mar 19th, 2022–Mar 20th, 2022

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

Regions

Kootenay Boundary.

Avalanche danger will be highest during periods of strong solar radiation, affecting sun-exposed slopes and cornices.

Watch for wind slabs at upper elevations and adjust your travel plans according to the changing conditions of elevation, aspect, and time of day.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SATURDAY NIGHT: Snowing, 5-15 cm of accumulation. Moderate to strong westerly winds. Clearing in the early morning, 1500 m freezing level dropping to valley bottom with winds easing to light.

SUNDAY: Partially cloudy, cloud cover increasing in the afternoon. Light westerly winds. Freezing level rising to 1500 m.

MONDAY: Cloudy with light snowfall, up to 5 cm accumulation. Light to moderate westerly winds. Freezing level rising to 1500 m.

TUESDAY: Cloudy with light flurries. Moderate to strong westerly winds. Freezing level rising to 3000 m in the afternoon.

Avalanche Summary

Wind slabs are expected to be reactive to human-triggering in the alpine and exposed areas at treeline.

There have been some notable human-triggered avalanches in the Nelson area and in the South Columbia region in the past few days (read more in this blog). These have been larger storm slabs above weak layers, and we are uncertain whether these are signs of a developing persistent slab avalanche problem that could begin impacting northern and eastern parts of the Kootenay Boundary region.

On Friday, an operator south of Nelson reported a large slab avalanche, triggered by a helicopter landing initiating a cornice failure. This avalanche stepped down to a deeper weak layer in the upper snowpack, suggesting that these deeper layers are still possible to trigger with large loads.

Snowpack Summary

10 to 20 cm of new snow overlies last week's 30 to 50 cm of denser, more settled snow. New snow depths taper significantly with elevation, with moist and crusty surfaces below 1800 m and on south aspects into the alpine. 

There is uncertainty about how well last week's snow is bonding to underlying layers. In the Selkirks, especially north of Nelson, it appears this snow could be bonding poorly to underlying crust and surface hoar layers. In the Monashees, it appears this snow has formed a stronger bond to underlying crusts. At this point, persistent slab problems could be developing in the deeper snowpack areas in the Selkirks. There are several other crust layers found 30 to 70 cm deep, and it appears the snow is mostly well bonded to these crusts.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Cornices become weak with daytime heating or solar exposure.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.