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Avalanche Forecast

Archived

Jan 5th, 2021–Jan 6th, 2021

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 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.

Regions

South Columbia.

Lots of recent fresh snow, strong southwest winds, and a buried weak layer means that human triggered avalanches remain likely for now. Choose conservative terrain.

Confidence

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

Weather Forecast

TUESDAY NIGHT - Cloudy with flurries, 5-10 cm / strong southwest wind / alpine low temperature near -7 

WEDNESDAY - Mainly cloudy with a few flurries, 5-10 cm / moderate southwest wind / alpine high temperature near -5 / freezing level 1400 m

THURSDAY - A mix of sun and cloud / light northeast wind / alpine high temperature near -7 

FRIDAY - Mainly sunny / light southeast wind / alpine high temperature near -2

Avalanche Summary

Recent 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 size 1-2 human and explosives triggered storm and wind slab avalanches were reported on Monday. 

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.

On Sunday, numerous natural, human and explosive triggered storm slab avalanches up to size 3.5 were reported in the region. Check out this MIN report from Sunday of an avalanche below treeline on Begbie Shoulder.

On Saturday, numerous natural and human triggered storm slabs to size 1 at treeline and below were reported.

Snowpack Summary

20-40 cm of recent fresh snow brings storm snow totals to around 40-80 cm. Strong southwest winds overnight have likely formed widespread storm slabs. In many areas, the storm snow sits on a weak layer of surface hoar that was buried around Christmas. This layer continues to be of concern, mainly at treeline and below treeline.

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 may vary 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, primarily at treeline and below.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • 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.