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Avalanche Forecast

Archived

Dec 30th, 2019–Dec 31st, 2019

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

Regions

Cariboos.

Forecast new snow amounts might not be be enough to create HIGH danger on their own, but they are adding to a layer that has begun to show a troubling degree of reactivity. It's time to adopt a mindset of stepping back to simple terrain while the snowpack adjusts.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday night: Cloudy with flurries bringing 10-20 cm of new snow. Strong southwest winds.

Tuesday: Cloudy with continuing flurries bringing 5-10 cm of new snow and new snow totals to 15-30 cm, increasing overnight. Moderate southwest winds. Alpine high temperatures around -4. 

Wednesday: Mainly cloudy with continuing flurries bringing 5-10 cm of new snow and 2-day snow totals to 30-50 cm, continuing overnight. Moderate southwest winds. Alpine high temperatures around -5.

Thursday: Mainly cloudy with isolated flurries and a trace of new snow. 3-day snow totals of 35-60 cm. Light to moderate west winds easing over the day. Alpine high temperatures around -14.

Avalanche Summary

Reports from the weekend included several notable MIN reports from the Barkerville area, where shooting cracks, whumphing, and both natural and machine triggered storm slabs were observed failing on our most recent surface hoar layer. One of these reports included a large (apparently older) persistent slab release near a large glide crack. 

Reports from the interior of the region on Saturday included other observations of several recent small (size 1.5) natural wind slab releases. These occurred between 1800-2300 metres on steeper northeast aspects and featured crown depths of up to 40 cm.

Snowpack Summary

A new layer of large surface hoar has been observed on the surface in sheltered areas of the region with a thin sun crust observed on many steep, sun exposed aspects. These surfaces are now being buried. 

Below the surface, 15-30 cm of recent snow has been either blown into soft wind slabs in alpine lees or remains low density. The interface below this snow may present as surface hoar on sheltered, shaded aspects, as a sun crust on steep sun-exposed aspects or as a more widespread melt-freeze crust below about 1700 metres. Reactivity at this layer has been noted in several recent MIN reports.

Below this interface, 60 to 120 cm of older storm snow is resting on a widespread layer of large, feathery, surface hoar from mid-December. This layer was a primary failure plane in the large natural avalanche cycle observed last week. Activity on this interface has tapered off, but there is concern for loading from forecast snowfall to reinvigorate avalanche activity at this depth.

A weak layer formed in late November is now buried around 1 m or more below the surface. Concern for this layer is limited to variable snowpack depth areas in the high alpine where it most likely exists as a combination of facets and crust.

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.