Avalanche Forecast

Archived

Dec 20th, 2020–Dec 21st, 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 now 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.

Weather Forecast

Looks like we’re moving into a bit of a clearing trend this week.

SUNDAY NIGHT: Freezing level lowering to valley bottom, moderate west/southwest wind, 1 to 5 cm of snow possible.

MONDAY: Broken cloud cover, freezing level at valley bottom, light variable wind, a few cm of snow possible.

TUESDAY: Broken cloud cover, freezing level near valley bottom, light northerly wind, no precipitation expected.

WEDNESDAY: Broken cloud cover, freezing level near valley bottom, 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.

On Friday natural slab avalanches to size 3 were reported on all aspects.

Snowpack Summary

An active storm cycle has produced 50 to 90 cm of storm snow over the last week which rests on a weak layer of surface hoar in many areas. This new snow has combined with south/southwest wind to form reactive slabs which are especially problematic at higher elevations.

A weak layer that was buried in early December is now down 50-110 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

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.