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Avalanche Forecast

Archived

Dec 4th, 2020–Dec 5th, 2020

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

Regions

Kootenay Boundary.

  

Above freezing temperatures up high over night and into the day Saturday will continue to stress the snowpack. Consecutive hot days are increasing the likelihood of triggering large avalanches on a crust near the bottom of the snowpack.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

  

FRIDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature 0 / Strong temperature inversion with above freezing air 2000-3500 m.

SATURDAY: Sunny / Moderate, south ridgetop wind / alpine high temperature +5 / Strong temperature inversion with above freezing air 2000-3500 m. dissipating in PM.

SUNDAY: Mix of sun and cloud / Light, west ridgetop wind / alpine high temperature -3 / Freezing level valley bottom.

MONDAY: Cloudy / Strong, southwest ridgetop wind / alpine high temperature -3 / Freezing level valley bottom.

Avalanche Summary

No recent avalanches reported on Thursday.

On Wednesday, numerous loose wet avalanches were reported from NE slopes above 2000 m. These avalanches were up to size 1.5 with no significant propagation.

Have you been out and about in the mountains? If so please submit to the Mountain Information Network (MIN). It doesn't have to be technical it can be as simple as a photo. Photos are especially helpful! 

Sending a big thank you to the already submitted MIN's this season. Thanks everyone!

Snowpack Summary

Recent sun and warm air in the alpine likely had the greatest impact on the upper snowpack, showing signs of instability and promoting further slab development and cohesion. This may be most concerning where these slabs sit above an old thin crust (down 15 cm) on south aspects and feathery surface hoar crystals in wind-sheltered areas. 

Northerly aspects will likely see fresh wind slab development at upper elevations on leeward slopes and melt-freeze conditions may exist on solar aspects at upper elevations. New surface hoar formation can be found mostly at treeline and below where it was protected from the warm temperatures, sunshine and wind.

Treeline snowpack depths sit around 50 to 80 cm in the south of the region. 

Crusts from mid-and early-November are generally found 30 cm below the snow surface and 10 cm up from the ground at all elevations. While they are showing resistant planar results in snowpack tests, a lot of uncertainty still exists with limited observations.

Terrain and Travel

  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.

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.