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Avalanche Forecast

Archived

Dec 22nd, 2021–Dec 23rd, 2021

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

Regions

North Columbia.

The current storm will continue until Thursday evening. In areas where you see more than 30 cm new snow, increase the danger rating to HIGH. 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

A unique situation of weather setting up as two systems, one from the north and one from the south, is pushing into the region through late Thursday night, bringing consistent snowfall amounts. Arctic air will return on early Friday, with bitterly cold conditions for the weekend.

WEDNESDAY NIGHT: Heavy snow 10-15 cm/ Strong to extreme southerly wind / Low -8 

THURSDAY: Snow 10-15 cm/ Moderate to strong west wind / High of -10

FRIDAY: Flurries 5 cm / Light southwest wind / High of -15

SATURDAY: Flurries 5 cm / Light southwest wind / High of -18

Avalanche Summary

Few observations were reported Wednesday due to poor visibility. Wind slabs were reactive to skier traffic and were up to 40 cm in thickness. Natural dry loose avalanches (size 1.5 - 2) were also reported from low-density snow on steep slopes at treeline and below treeline. 

If you go out in the mountains, please consider filling out a Mountain Information Network report.

Snowpack Summary

Touchy soft storm slabs are forming on slopes where accumulation are exceeding 30 cm. Recent strong alpine wind has created wind slabs in alpine and on cross-loaded features. Prior to this storm, cold temperature in the valley weak surface snow grains (surface hoar) were observed on isolated sheltered slopes at treeline and below.

A widespread crust, formed in early December, reaches as high as 2200 m and now sits 100-150 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. In areas where the crust is buried deeper than one meter, it starts to decompose and show sporadic reactivity.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.