Avalanche Forecast

Archived

Jan 2nd, 2021–Jan 3rd, 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 unlikely, human triggered possible.

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.

Regions

Kootenay Boundary.

Overnight snowfall and wind have likely formed widespread storm slabs which may become increasingly reactive with shifting wind and sun forecast for Sunday.

We recommend sticking to simple terrain while the new snow settles and buried weak layers adjust to the new load.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Saturday night: Snow, 10-30 cm, heaviest snowfall near Kootenay Pass, strong southwest wind, freezing level 1400 m.

Sunday: Flurries up to 5 cm then clearing, moderate northwest wind, alpine high temperature near -5, freezing level 1300 m.

Monday: Snow, 5-15 cm, moderate south wind, alpine high temperature near -3, freezing level 1300 m.

Tuesday: Sunny, light southwest wind, alpine high temperature near -7, freezing level 1100 m.

Avalanche Summary

Numerous size 1-2 explosive triggered storm slab avalanches were reported in the region on Thursday and Friday. Storm slab avalanche activity is expected to continue into Sunday. Predictable triggers include humans, wind and solar radiation.

With new snow slowly but steadily piling up, the chances of a resurgence of persistent slab avalanches will increase. This incremental loading will likely make it difficult to predict when this layer may once again reach a tipping point and start producing avalanches. This problem is best managed with conservative terrain selection.

Snowpack Summary

10 to 30 cm of new snow is expected between Saturday night and Sunday afternoon, bringing storm totals to 30-60 cm. As winds shift from southwest to northwest on Sunday, wind loading patterns will continue to change at upper elevations.

Two weak layers are buried in close proximity to one another. They are 70-100 cm deep around Nelson and 50-80 cm deep around Rossland and other western parts of the region. The layers are composed of feathery surface hoar and sugary faceted grains and they overlie a hard melt-freeze crust.

Terrain and Travel

Be careful to keep storm day fever from luring you out into bigger terrain features.
Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Avoid freshly wind loaded terrain features.
Even brief periods of direct sun could produce natural avalanches.

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.