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Avalanche Forecast

Archived

Feb 6th, 2021–Feb 7th, 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 unlikely, human triggered possible.
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.

Regions

Northwest Coastal.

Persistent slab avalanches can be difficult to predict, so a conservative approach is recommended. 

Storm slabs may still be easy to trigger, especially in wind loaded areas. Watch for a change in wind loading patterns with northerly winds.

Confidence

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

Weather Forecast

SATURDAY NIGHT - Mainly cloudy with isolated flurries / moderate northwest wind / alpine low temperature near -12 

SUNDAY - Sunny with cloudy periods / moderate to strong northwest wind / alpine high temperature near -12

MONDAY - Mainly sunny / light to moderate northwest wind / alpine high temperature near -16

TUESDAY - A mix of sun and cloud / moderate to strong northwest wind / alpine high temperature near -20

 

Avalanche Summary

At the time of publishing, there was a report of one size 2 human triggered persistent slab avalanche on a north aspect at 1200 m on Saturday.

On Friday, numerous dry loose avalanches were reported up to size 2 during the storm in steep terrain. 

On Thursday, reports indicated several small features were reactive up to size 1 on the surface hoar that was buried in late January. I suspect that once the persistent slab gains more cohesion and stiffens, this problem may become more widespread. Even a small avalanche can catch you by surprise and have enough mass to push you into a terrain trap below. 

Snowpack Summary

40-80 cm of recent storm snow from the past week sits on a persistent weak layer. This persistent weak layer consists of surface hoar in locations sheltered from the wind, facets, and stiff wind affected snow at upper elevations (upper treeline and the alpine). At lower elevations, (lower treeline and below treeline), 10-30 cm of snow sits above isolated pockets of surface hoar and a crust that is more prominent on solar aspects. 

The mid-pack seems to be well settled. Deep persistent layers appear to have mostly become unreactive, with the exception of the Bear Pass area and the far reaches south of Kitimat. 

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch your sluff: it may run faster and further than you expect.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.