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Avalanche Forecast

Archived

Jan 22nd, 2023–Jan 23rd, 2023

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 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.

Regions

North Columbia, South Columbia, Grohman, Esplanade, Jordan, North Selkirk, Shuswap, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

Danger ratings may be decreasing, but the weak and volatile snowpack structure remains the same. Do not take this as an indication to step out into bigger terrain, there is still a very real potential for triggering large and consequential avalanches. Stay disciplined and remember that your best defence continues to be choosing conservative, low-consequence terrain.

Confidence

Moderate

Avalanche Summary

On Saturday in the neighbouring region to the north, a serious avalanche, presumed to have resulted in a fatality, occurred in the Oasis riding area south of Valemont. The avalanche was on a north-northeast aspect at 2100 m. It was remotely triggered and likely ran on the November facets near the bottom of the snowpack. This large avalanche (size 2.5) had a depth of 80 to 120 cm. There were several other reports of human-triggered avalanches from nearby areas.

On Saturday, a few large natural persistent and deep persistent slabs were observed in the region. Several size 1-2 natural wind slabs were observed as well.

A few concerning avalanches occurred last Thursday. The first took place in the far north of the region on a southwest-facing alpine slope. It was a natural size 3 running on the November facets.

The second was a size 3.5 vehicle remote in the Central Monashees. This avalanche was remotely triggered by a snowcat travelling across a rocky west-facing ridgeline. This avalanche also failed on the November facets. The crown was up to 3.5m deep.

The third was another vehicle remote also running on the November facets. This one was in the Selkirks on a south-through west-facing piece of terrain.

All of these very large avalanches occurred at upper treeline/lower alpine. Avalanches like these are most likely to be triggered on steep, shallow and previously undisturbed slopes.

Snowpack Summary

New snow continues to gradually accumulate. A layer of surface hoar may be found below 5-10 cm of recent snowfall as well as a sun crust on steep solar aspects. Westerly winds will continue to affect exposed terrain and form wind slabs near ridge tops. At lower elevations, a rain crust exists down 10 to 40cm, with reported elevations extending up to 2000 m around Nelson, 1700 m around Revelstoke.

Two persistent weak layers in the middle of the snowpack may remain reactive to human triggering. They are both surface hoar layers that formed in early January and are typically found 40 to 90 cm deep throughout the region. There are also some deeper facet and surface hoar layers that formed in December, but recent snowpack observations suggest they are strengthening.

The bottom of the snowpack is made up of large weak facets buried in late November, which has caused an atypical deep persistent slab problem for this region.

Weather Summary

Sunday night

Clear periods with snowfall in the early morning, trace to 5 cm of accumulation. Alpine temperatures drop to a low of -12 °C. Light westerly ridge wind. Freezing level at valley bottom.

Monday

Mainly cloudy with light snowfall, up to 5 cm of accumulation. Alpine temperatures reach a high of -8 C. Ridge wind northwest 20-45 km/h. Freezing level rises to 800 m.

Tuesday

Mainly cloudy with isolated flurries. Alpine temperatures reach a high of -8 °C. Ridge wind northwest 20-40 km/h. Freezing level 900 metres.

Wednesday

Mainly cloudy with isolated flurries. Alpine temperatures reach a high of -4 °C. Ridge wind northwest 15-30 km/h. Freezing level rises to 1000 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.

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.