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Avalanche Forecast

Archived

Dec 20th, 2019–Dec 21st, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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 Columbia.

It's a great weekend to hit the ski hill! Widespread avalanche activity is expected today. Avoid avalanche terrain.

Confidence

High -

Weather Forecast

FRIDAY NIGHT - Periods of snow, 10-20 cm / southwest wind, 20-40 km/h / alpine low temperature near -5

SATURDAY - Periods of snow, 15-25 cm / southwest wind, 20-40 km/h / alpine high temperature near -3 / freezing level 1000 m

SUNDAY - Cloudy with sunny periods / southeast wind, 10-20 km/h / alpine high temperature near -8

MONDAY - A mix of sun and cloud / northwest wind, 10-20km/h / alpine high temperature near -9

Avalanche Summary

With ongoing snowfall and strong winds expected on Saturday, a widespread avalanche cycle is likely to continue throughout the day.

Observations on Friday were limited due to intense storm conditions, but it is likely that a natural avalanche cycle was occurring throughout the day.

There were numerous reports on Thursday of natural, explosives and human triggered avalanches up to size 3. Many of these were triggered remotely.

Previous heavy snowfall resulted in an avalanche cycle on Tuesday and Wednesday. Numerous natural and human triggered avalanches up to size 2.5 were reported

Snowpack Summary

The storm rages on in the North Columbias with 10-20 cm overnight on Friday, and another 15-25 cm expected during the day on Saturday. By the end of the day on Saturday, this will make for a total of 40-75 cm of snow in 48 hours. Storm slabs are expected to be widespread and very reactive.

There is anywhere from 100-160 cm of snow on top of a widespread layer of large, feathery surface hoar crystals. With more snow continuing to accumulate above this layer, it will likely remain very sensitive to human-triggering.

A weak layer that formed in late November is now over 170 cm deep. This is the layer of concern relating to the persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. Below this, a variety of crusts from late October are buried deeper in the snowpack..

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.

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.