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Avalanche Forecast

Archived

Dec 19th, 2021–Dec 20th, 2021

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

North Columbia.

Don't let the desire for deep powder pull you into high consequence terrain. Keep making conservative choices at treeline, where a persistent slab problem still exists.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

An Arctic ridge of high pressure will continue to build into the Interior, bringing clear skies and cold conditions with outflow winds through Monday. 

SUNDAY NIGHT: Clearing skies/ Light northwest wind / Low of -20

MONDAY: Sunny / Moderate northwest wind / High of -16

TUESDAY: Increasing cloudiness / Moderate to strong southwest wind / High of -15

WEDNESDAY: Snow 5-15 cm / Strong southwest wind / High -15

More details can be found on the Mountain Weather Forecast.

Avalanche Summary

A widespread natural cycle of storm slabs was observed at all elevations during Saturday's storm, including a few large loose dry avalanches (size 2) running fast. Poor visibility restricted avalanche observations during most of the storm.

A naturally triggered size 2.5 persistent slab avalanche was observed in the Monashees on Wednesday on a West aspect at 2150 m. This avalanche failed on the early December facet/crust combo. It was 100 cm deep, a good example of the high consequence of triggering this layer.

 If you go out, make sure to report any observations on the Mountain Information Network.  

Snowpack Summary

The storm brought around 30-40 cm of new snow in the region, favoring the southeast areas with up to 50 cm. Significant strong southerly winds have formed touchy storm slabs in alpine and treeline, especially in wind-affected terrain. Many sluffs were skiers triggered in low-density snow on steep slopes. 

Below the new snow, the defining feature of the snowpack is a widespread crust that reaches as high as 2200m and now sits 80-150 cm below the surface. 

In some places, overlying snow is well-bonded to the crust, but in others, weak faceted grains have been observed above it. The facets above the crust are most prominent at treeline where the crust is thinner. 

The recent snow load has increased the likelihood of triggering this weak layer.

Terrain and Travel

  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

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.