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Avalanche Forecast

Archived

Dec 9th, 2020–Dec 10th, 2020

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

Regions

Northwest Inland.

Wind slabs may be reactive to human triggers at upper elevations. Heads up the winds are changing and reverse loading may build isolated wind slabs on opposite slopes due to East winds on Thursday.

Confidence

Low - Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region. Uncertainty is due to limitations in the field data.

Weather Forecast

The cooling and drying trend continues with overcast conditions throughout Thursday and some sunshine Friday/ Saturday. Alpine temperatures will remain cool at -8 and freezing levels will likely be in the valley bottom. Ridgetop winds will blow light tomorrow from the East then switch to the southeast and decrease to light values for Friday and Saturday.

Avalanche Summary

No new avalanches reported on Wednesday. 

On Monday, operators reported a significant persistent slab cycle believed from Sunday up to size 2.5. These avalanches were all from wind loaded features with cornice failures triggering the weak basal facets. These avalanches were near Tatlatui Provincial Park which is outside of the region to the East. However, the information is helpful and may somewhat prepare us for the future with additional snow load on the suspect basal weakness in the region.

Have you been out in the mountains? If so, we'd love to hear from you! You don't necessarily have to submit a technical report as a photo can say it all! Please share your observations on the Mountain Information Network (MIN). Thanks for submitting!

Snowpack Summary

Up to 20 cm of recent snow fell at upper elevations and may sit above a newly formed crust from December 6th. This new snow may have a poor bond to the underlying crust and be reactive to human triggering. Recent strong winds from the southwest may have sifted the new snow onto lee aspects and behind terrain features building isolated wind slabs.

In many treeline and below treeline areas, the combination of above freezing temperatures and rain saturated the entire snowpack. As a result, the snow has melted fast at lower elevations, and snowpack depths have seen rapid settlement. With the current cool conditions and freezing levels falling to the valley bottom I suspect a widespread melt-freeze crust may exist. 

At the base of the snowpack sits the early November crust with basal facets below. Currently, hard shear snowpack test results exist on this potential weak interface and should continue to be tracked as the snowpack builds. In areas north and east in the region, the bottom of the snowpack reportedly consists of a crust from early November and weak facets near the ground. These basal facets have produced very large deep persistent slab avalanches near the Ningunsaw and Tatlatui Provincial Parks. Although the extent of this snowpack structure in the region is not well-known, it may be more prevalent in colder, shallower areas north and east in the region. 

Snowpack depths vary substantially with aspect, elevation, and wind exposure. Below treeline the terrain may still be below the threshold for avalanches. 

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid freshly wind loaded terrain features.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.

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.