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Avalanche Forecast

Archived

Feb 17th, 2021–Feb 18th, 2021

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 possible, human triggered probable.
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

Cariboos.

Strong southwest wind is expected on Thursday which has the potential to quickly form touchy wind slabs. Seek out wind sheltered terrain, and please let us know what you're seeing if you're out tomorrow. Thanks!

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

WEDNESDAY NIGHT: Freezing level at valley bottom, light west/northwest wind, no snow expected.

THURSDAY: A few clouds at dawn building to broken cloud cover in the afternoon, strong south/southwest wind, trace of snow possible during the day with 1 to 5 cm expected Thursday night.

FRIDAY: Overcast, freezing level rising to about 1000 m, moderate to strong west/southwest wind, trace of snow possible during the day with 1 to 5 cm Friday night.

SATURDAY: Broken cloud cover, freezing level beginning at valley bottom rising to about 900 m, strong southwest wind, trace of snow possible during the day with 5 to 10 cm Saturday Night.

Avalanche Summary

No new avalanche activity to report from this week.

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. New 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 Strong southwest 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.
  • Wind slabs are most reactive during their formation.
  • 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.