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Avalanche Forecast

Archived

Feb 19th, 2021–Feb 20th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Cariboos.

If you cannot identify avalanche terrain do not enter the backcountry this weekend, if you can, stick to simple terrain that is not threatened by overhead avalanche hazard. Avalanche danger will be on the rise throughout the stormy day, be sure you have a safe exit planned.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

FRIDAY NIGHT: Freezing level at valley bottom, moderate to strong west/southwest wind, 5 to 15 cm of light density snow expected.

SATURDAY: Overcast, freezing level beginning at valley bottom rising to about 800 m, strong west/southwest wind, 4 to 8 cm of snow expected during the day with another 5 to 10 cm Saturday night.

SUNDAY: Overcast, freezing level beginning around 1000 m, rising to 1800 m early in the day, strong southwest wind, 2 to 8 cm of snow at upper elevations with rain in the valleys. 10 to 15 cm of snow is expected at upper elevations Sunday night.

MONDAY: Scattered cloud cover, freezing level beginning around 1500 m and holding there throughout the day, strong west wind, 1 to 5 cm of snow at upper elevations with light rain in the valleys.

Avalanche Summary

New snow is beginning to stack up and plenty more is on the way which may lead to a natural avalanche cycle as we progress through the weekend.

This surprisingly large human triggered avalanche from near Wells Wednesday is a great example of the strange conditions that are created by reverse wind loading. Huge thanks to the reporting party for sharing this with the community.  

Snowpack Summary

Southwest flow has started pushing some more serious precipitation our way. As of Friday afternoon the first wave of the storm has produced 3 to 7 cm around Barkerville and up to 30 cm around Blue River. There is now 15 to 45 cm of snow resting on an untested potpurri of weak layers including surgary facets, feathery surface hoar, and wind-affected snow that formed as a result of the cold, dry and windy drought period.

We've now got 40 to 80 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features like cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust.  

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.