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Avalanche Forecast

Archived

Dec 19th, 2020–Dec 21st, 2020

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

Regions

North Rockies.

Areas like Pine Pass and Renshaw are in an avalanche cycle -- see Avalanche Section for the gossip. Continue to avoid avalanche terrain: stick to low angle slopes or play on flats without overhead hazard hanging above you.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system. Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

No break in the storms quite yet.

SATURDAY NIGHT: 10 to 25 cm overnight, highest amounts on the westerly side of the mountains. Strong southwest wind. Freezing level near valley bottom.

SUNDAY: Wake up to new snow that fell overnight. Light snow and mostly cloudy during the day, continued moderate to strong southwest wind. Temps around -5 to -10 C near treeline.

MONDAY: Mix of sun and clouds, dry, light variable wind, and -10 C or colder temperatures.

TUESDAY: Very similar to Monday

Avalanche Summary

Pine Pass reports on Friday (courtesy of your local AvCan field team) included natural, accidental, and remotely triggered avalanches up to size 2.5. That's a big slide to get tangled up in -- one party of three were caught and partially buried (one up to the neck) or fully buried (with a deployed airbag). Slide were running at the bottom or the recent storm snow (down 40 cm) or last week's crust (65 cm deep). There was also a size 3 reported from Renshaw. Observations arelimited due to lack of visibility.

Snowpack Summary

Upper snowpack is made up of new or recent snow and with one more storm lined up to track through the storm snow will continue to build. The forecast wind will also build windslabs. In some areas in the north (Pine Pass, possibly Wolverine) there is surface hoar near the bottom of this recent snow -- which may be as deep as 50 or 60 cm.

Mid-pack is where you'll find a variety of crusts. Most reports haven't found them to be an issue.

Basal-pack, the basement also has some crusts. I suspect the layer to be potentially reactive in northern parts of the region, such as Pine Pass, but do not have observations to back this up.

Snow depths are approaching 200 cm around Pine Pass, Torpy and McBride and around 100 cm in the northeast around Tumbler Ridge.  

Terrain and Travel

  • Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
  • Avoid areas with overhead hazard.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.