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Avalanche Forecast

Archived

Jan 20th, 2023–Jan 21st, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia, South Columbia, Blue River, Clearwater, Premier, Grohman, Clemina, Jordan, North Monashee, North Selkirk, Shuswap, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

Continue to make conservative terrain choices and consider the consequences of an avalanche on a chosen slope. You may not see signs of instability but the layers are still there. Avoid shallow, steep, rocky slopes.

Confidence

Moderate

Avalanche Summary

A few concerning avalanches occurred on 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 snow cat traveling 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 three of these very large avalanches occurred at upper treeline/lower alpine. In addition to the above mentioned avalanches there were also several skier triggered wind slabs and smaller remotely triggered persistent slab avalanches.

Snowpack Summary

New snow is gradually accumulating above settled snow from last week's warm storm. Southerly winds have pressed exposed terrain and formed 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, and 1600 m around Valemount.

Two persistent weak layers in the middle of the snowpack 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

Friday Night

Mostly cloudy with flurries bringing trace amounts of new snow. Westerly winds decreasing throughout the night to light by early morning. A low of -10 at 1800m.

Saturday

Stormy with up to 10cm of new snow expected. Moderate to strong southwest winds and a high of -4 at 1800m.

Sunday

A mix of sun and cloud with the possibility of light flurries bringing trace amounts of new snow. Light to moderate northwest winds and a high of -7 at 1800m.

Monday

Cloudy with flurries bringing up to 5cm of new snow. Strong northwest winds and a high of -8 at 1800m.

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.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.

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.