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Avalanche Forecast

Archived

Dec 4th, 2020–Dec 5th, 2020

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

Regions

North Rockies.

It's going to be HOT! Sunny skies, 3500 m freezing levels, and alpine temperatures up to +5 are in the cards for Saturday. Choose low angle terrain on all aspects, especially on sun exposed slopes. 

Confidence

Low - Uncertainty is due to limitations in the field data. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Unseasonably warm temperatures are expected to continue through the weekend, with some snow in the forecast for Monday

FRIDAY NIGHT - Mainly cloudy with scattered flurries / southwest wind, 60-80 km/h / alpine low temperature near -1 / freezing level 2000 m

SATURDAY - Mainly sunny, possible valley cloud / southwest wind, 60-80 km/h / alpine high temperature near +5 / freezing level 3500 m

SUNDAY - A mix of sun and cloud with isolated flurries / southwest wind, 40-50 km/h / alpine high temperature near +1 / freezing level 2300 m

MONDAY - Flurries, 5-10 cm / southwest wind, 50-70 km/h / alpine high temperature near 0 / freezing level 1800 m

Avalanche Summary

Warm temperatures and sunny skies in the alpine on Saturday could cause an increase in avalanche activity. Pay special attention to the temperature, as avalanches will be more likely on all aspects with significant warming.

There was an avalanche fatality near Pine Pass on Saturday, November 28. Reports indicate a size 3 deep persistent slab avalanche at approximately 1600 m elevation on a northeast aspect. The avalanche was approximately 55 cm deep, 800 m wide and ran 400 m in length. The avalanche may have run on a weak layer of faceted crystals sitting on a crust that was buried in early November.

If you get out into the mountains this weekend, please consider sharing your observations on the Mountain Information Network.

Snowpack Summary

The snowpack is highly variable due to recent strong southwest winds. In some areas, the windward slopes have been stripped of any recent snow. On lee aspects, wind deposited snow drifts may be up to 90 cm deep. Fresh wind slabs may be reactive to human triggers.

A crust that was buried in early November is near the base of the snowpack. In some areas, weak, sugary facets are sitting on this crust. This layer is of most concern on steep terrain in thin snowpack areas.

Snow depths are approximately 150 cm in the northwest of the region (Pine Pass), 180 cm in the south (Renshaw, Kakwa) and 100 cm in the the northeast (Tumbler ridge).  

Terrain and Travel

  • Avoid sun exposed slopes, especially if snow surface is moist or wet.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.

Problems

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.

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.