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Avalanche Forecast

Archived

Feb 9th, 2021–Feb 10th, 2021

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 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.

Regions

North Columbia.

Triggering avalanches may be possible in specific wind-drifted features or on open slopes near treeline where a buried weak layer persists.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Brrrrrr! Cold and dry conditions persist under arctic air

Tuesday night: Partly cloudy with a few flurries, light westerly ridgetop wind, alpine high temperature -22 C.

Wednesday: Mix of sun and cloud, light northerly wind, alpine high temperature -26 C.

Thursday: Sunny, light to moderate northeast ridgetop wind, alpine high temperature -28 C. 

Friday: Sunny, moderate easterly ridgetop wind, alpine high temperature -20 C. 

Avalanche Summary

Several small to large (size 1-3) natural, human and machine triggered wind slab avalanches were reported over the last few days. These avalanches released on northeast through east through south aspects above 2000 m and broke 10-30 cm deep. A few of these wind slabs were triggered by cornice falls.

On Thursday, a large (size 2) skier-triggered persistent slab avalanche was reported near the Gorge area. This avalanche failed on a widespread layer of surface hoar buried 60 cm deep. While activity on this layer has decreased, this weak layer warrants assessment in open, sheltered slopes at treeline where this layer is likely pronounced and preserved. 

Numerous small (size 1-1.5) loose dry avalanches in unconsolidated snow have been reported in steep terrain.

Snowpack Summary

Up to 35 cm of low density snow over the weekend has combined with intermittent northwest winds to create wind slabs which may be possible to human trigger in specific lee features. In sheltered areas, cohesion-less powder may be prone to dry loose avalanches that can run far and fast in these cold, dry conditions. With clear skies, there is uncertainty as to how much direct sun on Tuesday might warm steep slopes midday given the frigid temperatures.  

60-100 cm of snow from the past week is settling over a reactive weak layer of surface hoar. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features that are below treeline. Snowpack tests results continue to show the potential for propagation on this layer, like this MIN report from north in the region on Sunday. 

A less reactive layer of surface hoar or facets buried in early January can be found down 80-130 cm.

The mid/lower snowpack is generally well settled and strong. 

Terrain and Travel

  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.