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Avalanche Forecast

Archived

Dec 21st, 2019–Dec 22nd, 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 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.

Regions

South Columbia.

With another round of fresh snow on Saturday night, avalanche hazard remains elevated. Continue to avoid avalanche terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

SATURDAY NIGHT - Mainly cloudy with flurries, 5-15 cm / southwest wind, 20-30 km/h / alpine low temperature near -9

SUNDAY - Mainly cloudy with isolated flurries, up to 5 cm / southeast wind, 10-20 km/h / alpine high temperature near -7

MONDAY - Mainly cloudy with scattered flurries, 5-10 cm / southwest wind, 10-20 km/h / alpine high temperature near -7

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

Avalanche Summary

Though the storm is tapering off, widespread fresh storm slabs are expected to remain reactive on Sunday.

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

Numerous natural, human and explosives triggered avalanches up to size 2 were reported on Friday.

There were numerous reports on Thursday of natural, explosives and human triggered avalanches up to size 2.5. Some of these were triggered remotely.

Snowpack Summary

The South Columbias are seeing the tail end of the recent storm with up to 15 cm Saturday night, and more flurries expected on Sunday. The region has seen 60-100 cm of new snow since Thursday night. Storm slabs are widespread and are expected to remain reactive on Sunday.

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 160 cm deep. This is the layer of concern relating to the listed 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

  • 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.