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Avalanche Forecast

Archived

Dec 21st, 2021–Dec 22nd, 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 possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Watch the winter storm carefully as storm slabs will develop throughout the day. Areas in the west of the region are the most likely to see high snowfall amounts. 

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, will push into the region early Tuesday evening through late Thursday, with increased amounts in the Monashees. Arctic air will return on early Friday, with bitterly cold and drier conditions for the weekend.

 

TUESDAY NIGHT: Snow 5-10 cm / Strong southwest wind / Low of -13 

WEDNESDAY: Snow 10-15 cm / Strong to extreme southwest wind / High -8

THURSDAY: Snow 10 cm / Moderate west wind / High of -12

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

Avalanche Summary

Few natural wind slab avalanches (size 1.5) released out of alpine convexities. Riders were also able to trigger soft slabs while skiing steep lee slopes at treeline elevations. With the next storm, the likelihood of avalanches will increase in many areas.

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

Snowpack Summary

Variable wind has affected the storm snow (20-35 cm) on alpine and treeline slopes, creating isolated small pockets of hard/firm slabs. Cold temperature was prone to develop weak surface snow grains, such as surface hoar, in sheltered areas at treeline elevation and below. 

The defining feature of the snowpack is a widespread crust that reaches as high as 2400 m and now sits 60-150 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 faceting is 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 rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.

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.