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Avalanche Forecast

Archived

Dec 23rd, 2019–Dec 24th, 2019

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.
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 recent storm was a massive one and the snowpack may take longer than usual to recover, especially with the presence of persistent weak layers. Choose conservative terrain and minimize overhead exposure to avalanche terrain as the potential still exists for large avalanches.

Confidence

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

Weather Forecast

MONDAY NIGHT - Cloudy with clear periods / southeast wind, 10-30 km/h / alpine low temperature near -11

TUESDAY - Cloudy with sunny periods and isolated flurries / southeast wind, 20-40 km/h / alpine high temperature near -10

WEDNESDAY - A mix of sun and cloud / light northeast wind / alpine high temperature near -10

THURSDAY - A mix of sun and cloud / light southwest wind, 20-50 km/h / alpine high temperature near -9

Avalanche Summary

The recent storm was a significant one, and there is a great deal of uncertainty at this time as to how quickly the snowpack will gain strength. Avalanche occurrences are tapering, but recent avalanches have been very large. Patience and conservative terrain selection is the best way to manage this uncertainty.

On Sunday, there were dozens of reports of natural, human and explosives triggered avalanches up to size 4. These were a mix of storm slab and persistent slab avalanches.

On Thursday, Friday and Saturday, there were numerous reports of natural, human and explosives triggered avalanches up to size 3.5. A number of these were triggered remotely.

Snowpack Summary

The North Columbias received upwards of 80 cm between Thursday night and Saturday night. Storm slabs are likely widespread and may still be reactive to human triggers.

There is anywhere from 100-160 cm of snow on top of a widespread layer of large, feathery surface hoar crystals. This layer has reportedly been responsible for numerous recent avalanches and may be reactive to human triggers.

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.
  • 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.