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Avalanche Forecast

Archived

Jan 7th, 2021–Jan 8th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

Though avalanche danger may be decreasing, the potential exists to trigger persistent slab avalanches. While these avalanches are becoming less likely, the consequences are high. The uncertainty associated with complex snowpacks is best managed with conservative terrain choices.

Confidence

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

Weather Forecast

THURSDAY NIGHT - Cloudy with clear periods / light to moderate southeast wind / alpine low temperature near -7 

FRIDAY - A mix of sun and cloud / moderate south wind / alpine high temperature near -5 

SATURDAY - A mix of sun and cloud / light southeast wind / alpine high temperature near -7 

SUNDAY - A mix of sun and cloud / light southeast wind / alpine high temperature near -6

Avalanche Summary

Storm slabs will likely be easiest to trigger in wind loaded areas, as well as in the trees where they may rest on a buried surface hoar layer.

Numerous natural storm slab avalanches size 2-3.5 were reported in the neighboring Glacier National Park region on Wednesday.

A few natural and human triggered storm slab avalanches size 1-2 were reported on Tuesday. Natural storm slab avalanches up to size 3 were also reported in the nearby Glacier National Park region on Tuesday.

It is notable that there were several human triggered avalanches reported at lower elevations in the neighboring Glacier National Park region on Monday. These avalanches highlight the potential to trigger avalanches in the trees. Reports of these can be viewed here, here, and here.

Snowpack Summary

Around 50-80 cm of recent fresh snow now sits on a weak layer of surface hoar that was buried around Christmas. This layer is most prevalent at treeline and below treeline. Previous moderate to strong winds have likely redistributed the new snow, creating storm and wind slabs.

Two persistent weak layers buried in early/mid-December are now down about 90-150 cm. The form and distribution of these layers are highly variable and conditions may differ significantly from one valley to the next. The first layer has been primarily reported as small surface hoar. The next layer has been reported as a thin freezing rain crust, surface hoar, or thick rain crust depending on elevation and location. This layer also remains a concern.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.