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

North Columbia.

Watch the winter storm carefully. 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 night, 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 to extreme southwest wind / Low of -12

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

THURSDAY: Snow 5-10 cm/ Moderate to strong west wind / High of -10

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

Avalanche Summary

Few natural dry loose avalanches were reported out of steep terrain (size 1) as well as numerous fresh wind slab avalanches out of alpine convexities. 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

Strong wind has affected the recent storm snow (30-40 cm) in upper elevation only and scouring some southerly alpine features. Meanwhile, 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 2200 m 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. 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.