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Avalanche Forecast

Archived

Dec 14th, 2020–Dec 15th, 2020

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

Regions

North Rockies.

Expect wind slabs to develop in exposed areas, especially on Wednesday as we see some new snow and strong winds.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

MONDAY NIGHT: Dry or light flurries. Treeline temperatures around -10 C. Moderate ridgetop winds southwesterly around 40 km/h.

TUESDAY: Flurries. Treeline temperatures around -8 C. Moderate ridgetop winds southwesterly around 40 km/h.

WEDNESDAY: Around 10 cm new snow. Treeline temperatures around -5 C. Strong ridgetop winds southwesterly 50-70 km/h.

THURSDAY: Around 10 cm new snow. Treeline temperatures around -10 C. Light northwesterly winds.

Avalanche Summary

No recent slab avalanche have been observed in this regions.

Snowpack Summary

Snow depths are approximately 150 cm around Pine Pass, Torpy and McBride and around 100 cm in the northeast around Tumbler Ridge. 

The alpine is heavily wind-affected and lower elevations are capped by a hard crust up to around 1300 to 1600 m. Sheltered areas at treeline may still have 5 to 20 cm of soft snow on the surface. 

A widespread crust layer that may have sugary faceted grains above it can be found at the bottom of the snowpack. Uncertainty remains about if and where this layer is a problem. Recent observations from the McBride area suggest the snow is well-bonded to this crust. Observations from around Tumbler ridge suggest ongoing concern for this layer in this zone. I suspect the layer to be potentially reactive in northern parts of the region, such as Pine Pass, but do not have observations to back this up. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

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.