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Avalanche Forecast

Archived

Mar 20th, 2022–Mar 21st, 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, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Make conservative terrain choices as recently buried weak layers have been reactive in the Selkirks and may exist in other areas.

Crusts on solar aspect are becoming more the norm. Dry snow will exist on the more shaded aspects but watch for wind slabs at higher elevations.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SUNDAY NIGHT: Mainly cloudy, light flurries. Light to moderate westerly winds. Freezing level dropping to 700 m.

MONDAY: Cloudy, isolated flurries, up to 5 cm of accumulation. Light to moderate westerly winds. Freezing level rising to 1500 m in the afternoon.

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

WEDNESDAY: Mainly cloudy, isolated flurries. Moderate to strong southwest winds. Freezing level rising to 2500 m in the afternoon. 

Avalanche Summary

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 slab avalanches above weak layers, failing on either a buried sun crust on solar-aspects, or surface hoar on shaded-aspects. This MIN report from an incident on Saturday near Whitewater is an example of this problem.

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 15 cm of recent snowfall 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. 

Last week's snow is bonding poorly to underlying layers in many areas. In the Selkirks, especially north of Nelson, it appears this snow is bonding poorly to the underlying sun crusts on solar aspects and surface hoar on shaded-aspects. In the Monashees, it appears this snow has formed a stronger bond to underlying crusts. There are several other crust layers found 50 to 100 cm deep, and 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.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Minimize your exposure time below cornices.

Problems

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.

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.