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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

South Columbia.

Don't let the desire for deep powder pull you into high consequence terrain. Keep making conservative choices, especially 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 north wind / Low of -19

MONDAY: Sunny / Light west wind / High of -15

 

TUESDAY: Increasing cloudiness / Moderate to strong west wind / High of -13

WEDNESDAY: Snow 5-15 cm / Strong southwest wind / High -10

More details can be found on the Mountain Weather Forecast.

Avalanche Summary

A widespread natural cycle of storm slabs was observed at all elevations on most steep features during Saturday's storm. Poor visibility restricted avalanche observations during most of the storm. 

On Tuesday, a skier triggered size 1.5 was reported on a North aspect at 2200m. This avalanche occurred on the early December crust/facet combo. The avalanche was triggered by the sixth skier to enter the slope.

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

Snowpack Summary

The storm brought around 20-35 cm of new snow in the region, favoring the northeast areas with amounts up to 45 cm. Significant strong southerly winds have formed touchy storm slabs, especially in wind-affected terrain. Many sluffs were triggered by skiers on steep slopes.

Below the new snow, the defining feature of the snowpack is a widespread crust that reaches as high as 2400 m and now sits 50-120 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 faceting is most prominent at treeline where the crust is thinner. 

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

Terrain and Travel

  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.