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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 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 unlikely, human triggered possible.

Regions

South 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. Calm to light southwest winds.

Monday: A mix of sun and cloud with cloud increasing over the day and light flurries beginning in the afternoon. Light to moderate southwest winds increasing over the day. Alpine high temperatures around -5.

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

Wednesday: Cloudy with continuing flurries bringing 5-10 cm of new snow and 2 day snow totals to 25-40 cm. Light to moderate southwest winds. Alpine high temperatures around -5.

Avalanche Summary

Reports from Saturday were mainly limited to small (size 1-1.5) natural and skier triggered dry loose sluffs in steep terrain. One size 1 skier triggered wind slab was observed in the alpine in the Revelstoke area.

Observations from the North Columbias included some larger wind slab releases, including one which triggered a very large, 3 metre-deep persistent slab on a high alpine face. 

The spectacularly large and destructive natural avalanche cycle observed during last week's big storm has for the most part ended, however, persistent slabs have continued to react to explosives and other large triggers and have been reported up to size 3.

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 that occurred during and after the big storm two weekends ago. Activity on this interface has largely tapered off and this layer is suspected to be trending towards dormancy.

A combination of surface hoar, crust & facets formed in late November is now over 170 cm deep and is has become 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.