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Avalanche Forecast

Archived

Jan 8th, 2020–Jan 9th, 2020

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.
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.

Although snowfall has tapered, avalanche conditions remain complicated and dangerous. Stick with conservative terrain choices and give the snowpack time to adjust.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Wednesday night: Decreasing cloud, moderate west wind, alpine temperature -16 C.

Thursday: Increasing cloud, isolated flurries with trace accumulations, light west wind, alpine high temperature -10 C.

Friday: Cloudy, 5-15 cm of snow, moderate south wind, alpine high temperature -10 C.

Saturday: Cloudy, 10-20 cm of snow, light south wind, alpine high temperature -9 C. 

Avalanche Summary

A widespread avalanche cycle occurred overnight and into Wednesday. Numerous large (size 2-2.5) and very large (size 3-3.5) avalanches released from natural, human, and explosive triggers in the storm snow. 

Prior to the storm, there were many reports of large (size 2-2.5) avalanches from both natural and human triggers releasing on surface hoar layers formed in late December across aspects and elevations. These avalanches were breaking 60-90 cm deep. Several of them were remote-triggered.

As the new snow settles, storm slab avalanches have the potential to step-down to these deeper layers, forming very large and destructive avalanches.

Snowpack Summary

The most recent storm delivered 40-70 cm of new snow across the region with moderate to strong southwest winds. Expect storm slabs to be especially touchy in lee terrain features where southwest winds have been drifting new snow into stiffer, more reactive slabs.

Two layers of surface hoar from late December are now buried 80-140 cm deep. These layers continue to produce large to very large avalanches across aspects and elevations with continued loading from snow and wind.

Snowpack depths at tree line now range from 180-280cm, with a well settled mid and lower snowpack.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very 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.