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Avalanche Forecast

Archived

Mar 5th, 2021–Mar 6th, 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

Northwest Coastal.

Storm slabs may be reactive to human triggering, especially in wind loaded areas, and at upper elevations. Watch for signs of instability such as whumpfing, cracking and recent avalanches.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT - Mainly cloudy with a few flurries, 5 cm / strong southwest wind / alpine low temperature near -4 / freezing level 800 m

SATURDAY - Mainly cloudy with a few flurries, 5 cm / moderate southwest wind / alpine high temperature near -4 / freezing level 800 m

SUNDAY - Mainly cloudy with isolated flurries / light south wind / alpine high temperature near -5 / freezing level 800 m

MONDAY - A mix of sun and cloud / light southwest wind / alpine high temperature near -4 / freezing level 800 m

Avalanche Summary

On Thursday, there were numerous reports ranging from 12-36 hours old. There was a fairly widespread natural wet-loose avalanche cycle reported at lower elevations throughout the region. There were also reports of widespread natural storm, and wind slab avalanches that ranged from size 1-3. Avalanches in the south of the region around Kitimat, Terrace, and along the Skeena corridor were generally in the size 1-2.5 range. The larger avalanches were observed further north in areas such as the Nass Valley, Bear Pass and closer to Ningunsaw. 

On Wednesday there were several size 1-2 explosive triggered storm slabs and wet loose avalanches reported in the north of the region, somewhat close to the Ningunsaw area.

On Tuesday, a notable natural size 3 persistent slab avalanche was reported on a south to southwest aspect along the Highway 16 corridor between Terrace and Prince Rupert. It is suspected to have failed on the mid-February persistent weak layer. 

Snowpack Summary

The region has received 60-100 cm of recent storm snow over the past week. This has been accompanied by strong southwest winds which have formed deep wind slabs on leeward slopes. Massive cornices exist on ridgelines at treeline and in the alpine. 

There is now 100-200 cm over two persistent weak layers that were buried in mid-February and late January. These layers consist of surface hoar in areas sheltered from the wind, and facets that developed during the cold snap. These weak layers have been the cause of several large avalanches in the past week. 

There are currently no layers of concern in the mid and lower snowpack.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.