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Avalanche Forecast

Archived

Dec 21st, 2019–Dec 22nd, 2019

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

Regions

North Columbia.

The brunt of the storm may have passed, but human triggered avalanches remain likely. The region has recently received a huge dump of new snow that may take some time to stabilize. Choose conservative terrain and avoid overhead exposure to avalanche terrain.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SATURDAY NIGHT - Mainly cloudy with scattered flurries / southwest wind, 20-30 km/h / alpine low temperature near -9

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

MONDAY - Sunny with cloudy periods / southwest wind, 10-20 km/h / alpine high temperature near -8

TUESDAY - A mix of sun and cloud / southeast wind, 20-40 km/h / alpine high temperature near -10

Avalanche Summary

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

There were numerous reports of natural, human and explosives triggered avalanches up to size 3.5 on Friday.

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

Snowpack Summary

The storm has finally abated in the North Columbias, which has received upwards of 80 cm since Thursday night. Storm slabs are widespread and are expected to remain reactive to human triggers on Sunday.

There is anywhere from 100-160 cm of snow on top of a widespread layer of large, feathery surface hoar crystals.

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. 

Terrain and Travel

  • Make conservative terrain choices and avoid overhead hazard.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.

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.