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Avalanche Forecast

Archived

Dec 29th, 2019–Dec 30th, 2019

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

Regions

Cariboos.

Our persistent slab problem has evolved into a low probability/high consequence scenario. Maintain diligent group management and keep avoiding classic weak points like shallow rocky start zones and steep convexities if you're venturing into bigger terrain.

Confidence

Moderate -

Weather Forecast

Sunday night: Clear periods. Light southwest winds.

Monday: Increasingly cloudy with flurries starting in the evening and 10-15 cm accumulating overnight. Strong southwest winds. Alpine high temperatures around -5.

Tuesday: Cloudy with flurries bringing approximately 5 cm of new snow, continuing overnight. Moderate south winds easing over the day. Alpine high temperatures around -6. 

Wednesday: Mainly cloudy with continuing flurries bringing 5-10 cm of new snow and 2 day snow totals to 25-35 cm. Moderate southwest winds. Alpine high temperatures around -5.

Avalanche Summary

Reports from Saturday included 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.

Small loose dry avalanches were observed out of extreme terrain over the weekend.

Last weekend there were reports of numerous natural and explosive triggered avalanches up to size 2.5

Snowpack Summary

Recent moderate westerly winds are likely to have blown around 15-30 cm of recent low density snow into soft wind slabs in alpine lees. 

Below the recent snow, 60 to 120 cm of older storm snow is resting on a widespread layer of large, feathery, surface hoar which we're calling the "December 12th Surface Hoar." This layer was the primary failure plane in the large natural avalanche cycle observed last week. Activity on this interface has tapered off, but there remains some uncertainty as to how quickly the snowpack is gaining strength.

A weak layer formed in late November is now buried around 1 m or more below the surface. This interface may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Caution around convexities or sharp changes in terrain.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.

Problems

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.

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.