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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

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 possible, human triggered probable.

Regions

North Columbia.

50 to 100 cm of recent storm snow rests on a smorgasbord of weak layers in our upper snowpack. It's time to scale the objectives way back and enjoy the simple pleasure of riding mellow well-supported treed features that are out of the wind and free of overhead hazard.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the limited number of field observations.

Weather Forecast

One last pulse tonight, and then it looks like we’re moving into a bit of a clearing trend this week.

MONDAY NIGHT: Freezing level near valley bottom, moderate to strong northerly wind, 5 to 15 cm of snow expected.

TUESDAY: Scattered cloud cover, freezing level at valley bottom, light northerly wind, no significant precipitation expected.

WEDNESDAY: A few clouds, freezing level at valley bottom, light southwest wind, no new snow expected.

THURSDAY: A few clouds, freezing level at valley bottom with potential for a light alpine temperature inversion, light southerly wind, no new snow expected.

Avalanche Summary

Over the weekend a natural avalanche cycle took place with avalanches averaging size 1.5 to 2.5, but there were a few size 3 and even size 3.5's in the mix too.

Snowpack Summary

An active storm cycle has produced 60 to 100 cm of storm snow over the last week. Underneath this storm snow there is a sandwich of weak layers which are widespread throughout the region.

Just under the new snow, down about one meter below the surface is the mid December surface hoar. This layer has been failing naturally and has been quite sensitive to human triggering throughout the storm cycle. Large avalanches have been running on this interface connecting big terrain features. 

Below that lies the early December persistent weak layer, it's about 80 to 140 cm below the surface. This weak layer is a mixed bag that often presents as surface hoar and facets sitting on top of a stout supportive crust. There are facets below the crust too. This is a nasty weak layer, when avalanches fail on it, they have been large and destructive. Smaller avalanches in motion can step down to this one too. This weak layer is going to haunt us for the foreseeable future. 

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Carefully manage your exposure to overhead hazards while entering and leaving riding areas.

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.