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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

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

Regions

North Columbia.

A warming trend means that slabs may become sensitive to human traffic. The warming also has the possibility of waking up a buried weak layer 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

SUNDAY NIGHT: Cloudy with isolated flurries, accumulation trace to 2 cm, moderate to strong southwest wind, alpine temperature -4 C, freezing level rising to 700 m.

MONDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, moderate to strong southwest wind, alpine temperature -5 C, freezing level 1200 m.

TUESDAY: Cloudy with snowfall, accumulation 5 cm, light to moderate south wind, alpine temperature -6 C, freezing level below valley bottom.

WEDNESDAY: Morning snowfall then a mix of sun and cloud, accumulation 2 to 5 cm, light southwest wind, alpine temperature -8 C, freezing level below valley bottom.

Avalanche Summary

A few small (size 1) storm slab avalanches were triggered naturally and by humans on Saturday. They were generally 10 to 20 cm thick and on all aspects

Although over a week old now, 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) last weekend. 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 on Monday with a rise in air temperature.

Snowpack Summary

Around 10 to 30 cm of snow has fallen in the past couple of days, with associated strong southwest wind. A rise in the air temperature on Sunday night into Monday will mean that the snow will form slab properties quickly. Expect the most reactive slabs to be in lee terrain features near ridges.

A layer of surface hoar buried 80 to 150 cm deep could still be a concern in certain parts of the Selkriks and the northern end of the Monashees. Although an avalanche has not been reported on this layer since January 13, the likelihood of triggering it may increase as the air temperature warms.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • 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.