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

Regions

North Columbia.

Our persistent slab problems are slowly fading, but it's key to remember the high consequences of triggering. 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

High -

Weather Forecast

Sunday night: Clear periods. Light southwest winds.

Monday: Becoming cloudy with isolated flurries bringing a trace of new snow during the day and increasing overnight. Light to moderate southwest winds increasing over the day. Alpine high temperatures around -7.

Tuesday: Cloudy with continuing flurries bringing new snow totals to 10-20 cm, continuing overnight. Light to moderate southwest winds. Alpine high temperatures around -7.

Wednesday: Cloudy with continuing flurries bringing 10-15 cm of new snow and 2 day snow totals to 35-50 cm, continuing overnight. Light to moderate southwest winds. Alpine high temperatures around -7.

Avalanche Summary

Reports from Saturday included a few observations of recent natural and skier-triggered wind slabs reaching size 2.5 (large). One wind slab release managed to trigger a very large (size 3) deep persistent slab on a steep, unsupported slope in the high alpine. Its crown fracture was 3 metres deep. All of the above occurred above 2200 metres.

The spectacularly large and destructive natural avalanche cycle observed during last week's big storm has for the most part ended but persistent slabs have shown continued reactivity to explosives and other large triggers.

Snowpack Summary

In exposed areas at higher elevations, recent moderate southwest winds have formed some isolated wind slabs with the 10-30 cm of low density snow we received late last week. Elsewhere this recent snow remains unconsolidated. The interface below it may present as a sun crust on steep sun-exposed aspects or as a more widespread melt-freeze crust below about 1700 metres.

100 to 160 cm of snow is now resting on a widespread layer of large, feathery, surface hoar from mid-December. This layer was the primary failure plane in the very large and destructive natural avalanche cycle observed during and after the big storm two weekends ago. Activity on this interface has largely tapered off and is this layer is suspected to be trending towards dormancy.

Another weak layer composed of a combination of surface hoar, crust & facets formed in late November is now over 170 cm deep and is presently inactive.

Terrain and Travel

  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid convexities, steep unsupported terrain and rocky outcroppings.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.