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Avalanche Forecast

Archived

Jan 18th, 2023–Jan 19th, 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 unlikely, human triggered possible.
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

West Purcell.

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.

Confidence

Moderate

Avalanche Summary

Avalanche activity has gradually slowed down after a widespread natural cycle occurred on Friday and Saturday. There were numerous large (size 2) human triggered avalanches on Sunday, and then on Monday there were fewer human triggered avalanches and they generally were smaller (size 1 to 1.5).

The previous natural cycle produced large to very large avalanches (size 2 to 3.5) at all elevations and aspects on multiple persistent weak layers. Most of the activity was on the two surface hoar layers from January, but there was also activity on the November facets near the bottom of the snowpack. Human triggered avalanches since the storm have primarily been on surface hoar layers buried 40 to 80 cm deep, many occurring in sparely forested terrain. A few large (size 1.5 to 2.5) deep persistent avalanches were triggered with heavy loads on Monday.

Snowpack Summary

New snow is gradually accumulating above settled snow from last week's warm storm. At lower elevations, a rain crust exists down 5 to 25cm, with reported elevations extending up to 2000 m around Nelson, 1700 m around Revelstoke, and 1600 m around Valemount. The snow surface will likely become moist on sun exposed slopes.

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 80 cm deep throughout the Columbias. 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

Wednesday Night

Cloudy with around 5cm of new snow expected. Light to moderate southwest winds and a low of -7 at 1800m.

Thursday

A mix of sun and cloud with the possibility of light flurries bringing trace amounts of new snow. Light northwest winds and a high of -6 at 1800m.

Friday

A mix of sun and cloud with flurries bringing a few centimeters of new snow. Moderate to strong northwest winds and a high of -7 at 1800m.

Saturday

Cloudy with up to 10cm of new snow. Moderate to strong southwest winds and a high of -6 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.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.

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.