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Avalanche Forecast

Archived

Dec 15th, 2020–Dec 16th, 2020

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

Regions

North Columbia.

20-40 cm of new snow with southwest winds have likely formed reactive storm slabs. Choose conservative terrain and watch for signs of instability such as whumphing, cracking and recent avalanches.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

TUESDAY NIGHT - Cloudy with flurries, 5-10 cm / southwest wind, 25-50 km/h / alpine low temperature near -8

WEDNESDAY - Mainly cloudy with isolated flurries, 5 cm / southwest wind, 20-40 km/h / alpine high temperature near -7 

THURSDAY - Flurries, 5-15 cm / southwest wind, 20-40 km/h / alpine high temperature near -7

FRIDAY - Periods of snow, 15-20 cm / southwest wind, 30-60 km/h / alpine high temperature near -7

Avalanche Summary

With 20-40 cm of new snow and moderate to strong southwest winds, human triggered avalanches are likely, especially in wind loaded areas.

Snowpack Summary

20-40 cm of snow has fallen in the region since Monday afternoon. This new snow has buried a weak layer of surface hoar in many areas. Moderate to strong southwest winds will mean that this new snow will likely form reactive slabs.

A weak layer that was buried about a week ago is now down 40-60 cm. This layer is variable and has been reported to exist as either a crust or surface hoar. In any case, it is a persistent weak layer with a significant load above it now, and it may react easily to human triggers.

Another crust that was buried in early November can be found near the base of the snowpack. There have been no recent avalanches reported on this layer, however it may be possible to trigger it from shallow, rocky terrain.

Terrain and Travel

  • Choose conservative terrain and watch for clues of instability.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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.