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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

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

Regions

Kootenay Boundary.

Avoid avalanche terrain during heavy snowfall and strong winds. Minimize your exposure to overhead hazard as avalanches may run into lower elevations.

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

TUESDAY NIGHT: Mixed precipitation continues overnight with 10mm expected. Freezing levels remain above 2000m overnight with strong southwest winds. 

WEDNESDAY: 10-25mm mixed precipitation with strong southwest winds. Accumulations favour the Nelson area, however freezing levels will reach 2500m early in the day and remain high.

THURSDAY: Precipitation tapers early in the morning to clearing skies. Winds shift to moderate westerlies. Alpine high of -5, freezing level at 1800m, dropping to valley bottom overnight.

FRIDAY: Clear with moderate westerly winds. Freezing level remains below 1000m. 

Avalanche Summary

On Saturday November 27, a size 2 storm slab was observed near Whitewater in a steep north facing treeline feature, unknown trigger.

On Friday, an avalanche cycle size 1-2 was observed from north facing alpine start zones. A size 1.5 skier accidental storm slab was also reported on the Mountain Information Network near Nelson. They noted a fast moving avalanche with wide propagation, supported by a hard bed surface.

Note that there are very few field observations in the Kootenay Boundary this early in the season. Backcountry users need skills in assessing conditions and decision making. If you go out in the mountains, please share your observations and/or photos on the Mountain Information Network.

Snowpack Summary

Overnight snow falls on a moist upper snowpack with around 30cm of recent storm snow. A series of rain crusts formed over the last week exist in the upper snowpack, each separated by up to 10cm of moist snow.

The mid-November crust is down 40-80cm and is up to 10cm thick. The lower snowpack is a series of crust and facet layers. At the bottom of the snowpack, up to 20 cm of faceted snow may be found. 

Snowpack depths at treeline range from 50-100 cm, with alpine depths exceeding 150 cm in areas. Below 1700m, snowpack depths decrease rapidly. The entire snowpack will likely be saturated at lower elevations. 

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.