Avalanche Forecast

Archived

Dec 29th, 2020–Dec 30th, 2020

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, 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

Kootenay Boundary.

With fresh snow on the way keep in mind we are concerned about buried weak layers. Cautious terrain selection remains important.

Confidence

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

Weather Forecast

A weak frontal system crosses the region on Wednesday then a bigger system is poised to hit the region on the weekend.

TUESDAY NIGHT: Increasing cloud with snow starting around 3 am, moderate southwest wind, temperatures around -8 C.

WEDNESDAY: Flurries with 5-10 cm of snow, moderate southwest wind, temperatures around -6 C.

THIURSDAY: Flurries end early in the morning then mostly cloudy in the afternoon, moderate west wind, temperatures around -5 C.

FRIDAY: Flurries starting midday with a trace of new snow by the end of the day, moderate south wind, temperatures around -5 C.

Avalanche Summary

No new avalanches were reported on Monday, but a few skier triggered size 1 slab and loose avalanches were reported over the weekend. Many storm and persistent slab avalanches were observed last week. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and at elevations between 2000 and 2300 m. Although avalanche activity appears to have diminished, I wouldn't rule out the possibility of seeing more persistent slab avalanches.

Snowpack Summary

Stormy weather on Wednesday will bring 5-10 cm of new snow and could form new wind slabs in leeward terrain. Two weak layers are buried in close proximity to one another. They are 50-80 cm deep around Nelson and 30-50 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 overly a hard melt-freeze crust. There was substantial avalanche activity on these layers prior to Christmas from natural and human triggers. Although reports of such avalanches have been dwindling, these weak layers remain a concern, as they can produce large and destructive avalanches.

Terrain and Travel

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.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.