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Avalanche Forecast

Archived

Feb 16th, 2021–Feb 17th, 2021

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

Regions

Cariboos.

Newly wind-drifted snow and lingering buried weak layers warrant assessment on Wednesday if you travel in avalanche terrain.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

TUESDAY NIGHT: Decreasing cloud, light flurries with a trace of snow, moderate northwest wind, alpine temperatures around -16 C.  

WEDNESDAY: Mix of sun and cloud, moderate northwest wind at ridgetop, alpine temperatures around -14 C. 

THURSDAY: Increasing cloud, strong south wind, alpine high temperatures around -8 C. 

FRIDAY: Mostly cloudy, light flurries with up to 5 cm of snow, strong southwest wind, alpine temperatures around -10 C.

Avalanche Summary

Over the weekend, observers reported several small human-triggered wind slabs at treeline and alpine elevations in areas west in the region (see the MIN reports here and here). A MIN report near Valemount reported small loose dry avalanches on steep terrain in the trees.

Earlier in February, there was widespread avalanche activity on a weak layer of buried surface hoar, mostly on treeline features (see some photos in the MIN reports here, here, and here). 

Snowpack Summary

Light flurries have begun to accumulate over a variety of surfaces including surgary facets, feathery surface hoar, and wind-affected snow that formed as a result of last week's dry, cold weather. Snow totals ranging from 10-15 cm may be found in areas west and north in the region, with 5 cm falling in the south and east of the region. Moderate northwest winds at ridgetop are expected to build fresh wind slabs that may be possible to trigger. Lingering wind slabs from last week's wind-loading events are trending unreactive. 

40-70 cm of snow from February is settling over a reactive weak layer of surface hoar buried in late January. In some areas, there may be two of these layers in close proximity (buried Jan 24th and Jan 30th). Reactivity on these surface hoar layers has primarily been observed at treeline and in "treeline-like" features, like cutblocks, that are below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust.  

Additional weak layers may present in the lower snowpack, but are not a concern in most areas until we see significant snow loading or rapid warming. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Extra caution is needed around cornices under the current conditions.

Problems

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.

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.