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Avalanche Forecast

Archived

Jan 18th, 2020–Jan 19th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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.

Fresh slabs are expected to grow and become more sensitive as snow falls, the wind continues to blow, and the air temperature increases. There still remains a possibility of triggering a buried weak layer, particularly in the eastern and northern parts of the region.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

SATURDAY NIGHT: Cloudy with snowfall, accumulation 5 cm, moderate to strong southwest wind, alpine temperature -8 C, freezing level below valley bottom.

SUNDAY: Cloudy with snowfall, accumulation 5 to 15 cm, moderate to strong southwest wind, alpine temperature -6 C, freezing level rising to 700 m.

MONDAY: Increasing clouds with afternoon snowfall, accumulation 1 to 3 cm, moderate to strong southwest wind, alpine temperature -3 C, freezing level 1000 m.

TUESDAY: Cloudy with snowfall, accumulation 5 cm, light southeast wind, alpine temperature -6 C.

Avalanche Summary

A few wind slab avalanches were reported in the region on Friday at treeline and alpine elevations. They ranged from small (size 1) to large (size 2 to 3) and were triggered naturally and by humans. They most often occurred on northwest, north, and east aspects and had slab depths ranging from 15 to 80 cm.

Last weekend there were a few notable reports of large persistent slab avalanches in the Selkirks and the northern tip of the Monashees (near Blue River and Valemount). The avalanches failed on a 100 cm deep surface hoar layer on north and east aspects between elevations of 1200 to 2100 m. Observations suggest this layer has trended towards being less reactive. There is uncertainty on whether the layer will wake up with more snowfall and a rise in air temperature.

Snowpack Summary

Strong southwest wind and around 10 to 20 cm of new snow will form fresh storm slabs, with the most reactive slabs being in lee terrain features at higher elevations. The slabs may develop quickly due to relatively warm air temperature.

A layer of surface hoar is now buried 80-150 cm below the surface and could still be a concern in certain parts of the Selkriks and the northern end of the Monashees. A facet/crust layer from late November lingers near the bottom of the snowpack and has occasionally been reactive in isolated shallow snowpack areas.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

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.