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Avalanche Forecast

Archived

Feb 12th, 2023–Feb 13th, 2023

Alpine
Natural avalanches possible, human triggered probable.
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 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.

Regions

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

Forecast snowfall amounts are enough to create dangerous avalanche conditions for Monday, but surface instabilities will be overlapping several problematic snowpack layers that are consistently being indicated in recent step down and even remotely triggered avalanches. It's a good day to back off from avalanche terrain while the snowpack decides how to react to the latest load.

Confidence

Moderate

Avalanche Summary

Among several natural and human triggered wind slabs and storm slabs (as large as size 2.5), Friday and Saturday's reports also included a few notable observations of step down avalanches and remotely triggered avalanches involving persistent weak layers.

On Saturday just west of Frisby ridge, an aircraft remotely triggered a 70 cm-deep persistent slab on a steep roll in a below treeline opening from 100 metres away. On Friday we saw a cornice release that triggered a small pocket to the basal snowpack in the South Monashees while another report from the central Monashees details wind slabs in several instances stepping down to one of several midpack layers covered in our snowpack summary.

It seems right now that any surface avalanche or cornice drop stands a very good chance of stepping down to a weak layer.

Snowpack Summary

Another 15-35 cm of new snow should accumulate in the region by end of day Monday with amounts once again greatest in the north of the region.

The new snow will add to about 60-100 cm of storm snow from the past week, arriving most recently with strong southwest winds. These increasing storm totals are sitting above wind-affected surfaces and a crust that extends up to 1800 m in the northern part of the region and up to 2000 m further south. Small facets may be found above the crust. This layer warrants close monitoring as we move through the period where a critical load and slab properties may develop over it.

Deeper in the snowpack two layers of surface hoar which formed in early January are now roughly 80 to 140 cm deep. Although snowpack tests are indicating strengthening here, these weak layers are still being watched closely by local operators and may be associated with recent isolated step-down avalanches.

Large and weak facets from November are near the base of the snowpack and although avalanche activity on this basal weakness has been on a bit of a decline, it still figures prominently in the assessments and terrain use (and avoidance) of professionals throughout the region.

Weather Summary

Sunday night

Cloudy with increasing snowfall bringing 10-25 cm of new snow, greatest in the north of the region. Moderate to strong southwest winds.

Monday

Cloudy with easing but convective flurries bringing 5-10 cm of new snow, again greatest in the north of the region. Light to moderate southwest winds, easing over the day. Treeline high temperatures around -6.

Tuesday

A mix of sun and cloud with isolated flurries. Light northwest winds. Treeline high temperatures around -7.

Wednesday

A mix of sun and cloud. Light southwest winds. Treeline high temperatures around -7.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.

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.