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Avalanche Forecast

Archived

Jan 1st, 2021–Jan 2nd, 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 and human triggered avalanches likely.
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.

Regions

Kootenay Boundary.

Storm slabs will likely be building and becoming increasingly reactive throughout the day with new snow and wind.

A persistent weak layer from December may "wake up" this weekend and produce avalanches again with the new snow load. Maintain a conservative approach to terrain.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast snowfall amounts are uncertain.

Weather Forecast

FRIDAY NIGHT - Snow, 10-15 cm / southwest wind 30-60 km/h, gusting to 80 km/h / alpine low temperature near -4 / freezing level 1000 m

SATURDAY - Snow, 10-15 cm, with another 15-20 cm overnight / southwest wind 40-60 km/h / alpine high temperature near -3 / freezing level 1100 m

SUNDAY - Snow, 5-10 cm / southwest wind 30-50 km/hr / alpine high temperature near -3 / freezing level 1500 m

MONDAY - Snow, 10-15 cm / southwest wind, 20-30 km/h / alpine high temperature near -3 / freezing level 800 m 

Avalanche Summary

Storm slabs may become increasingly reactive throughout the day on Saturday as the new snow adds up.

With new snow piling up over the weekend, the chances of a resurgence of persistent slab avalanches will increase. Without a big dump of snow over a short period of time, 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.

There were numerous size 1-2 explosives triggered storm slab avalanches reported in the region on Thursday.

Snowpack Summary

20-30 cm of new snow is expected between Friday night and Saturday afternoon, bringing total recent snow amounts to 30-50 cm. Storm slabs will likely be building throughout the day.

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. 

The new snow load expected over this weekend will likely increase the chances of large avalanches running on this layer. 

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Use conservative route selection and resist venturing out into complex terrain.

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.