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Avalanche Forecast

Archived

Jan 5th, 2021–Jan 6th, 2021

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

Regions

Northwest Coastal.

Avalanche danger remains HIGH as the storm rages on. Avoid all avalanche terrain during periods of heavy snowfall and wind.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

The storm rages on until Wednesday morning then light flurries continue.

TUESDAY NIGHT: 15-25 cm of snow, strong southwest wind, treeline temperatures around -4 C.

WEDNESDAY: Scattered flurries continue with 10-20 cm of snow throughout the day, strong southwest wind, treeline temperatures around -2 C.

THURSDAY: 5-10 cm of snow by the morning then clearing skies in the afternoon, strong south wind, treeline temperatures around -5 C.

FRIDAY: Cloudy skies and isolated flurries with up to 5 cm of snow, moderate south wind, treeline temperatures around -5 C.

Avalanche Summary

Avalanche activity has been reported continuously since New Year's Day, with widespread natural size 2-3 storm slab avalanches at all elevations and numerous human triggered avalanches in the Shames and Terrace area (see photos in these MIN reports). The human triggered avalanches have been size 1-2 and roughly 30-70 cm deep, and have shown signs of failing on a reactive weak layer beneath the storm snow (e.g. surface hoar and crusts). Reports suggest recent avalanches have only involved snow that has fallen since New Year's, with the exception of a few explosive triggered avalanches that stepped down to deeper weak layers.

Snowpack Summary

A non-stop series of storms are building thick storm slabs. 75-125 cm of snow has fallen since New Year's Day and another 20-40 cm is expected on Wednesday. Given the intensity of the storm we expect a natural avalanche cycle in the newest snow, and are uncertain about whether the other metre of recent snow has settled or is still going to produce avalanches. Reports from the Shames area suggest the storm snow has been reactive and bonding poorly to crust and surface hoar layers that are now an estimated 60-120 cm deep.

There were some deeper weak layers that were problematic around Christmas, including a surface hoar layer and a melt-freeze crust with weak facets around it. These layers were particularly problematic in the Nass Valley, Sterling, and Beaupre riding areas. These layers are now 100-200 cm deep and could be stressed by the intense load of the new snow, but will likely be inactive once the storm ends.

Terrain and Travel

  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Storm slabs in motion may step down to deeper layers resulting in 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.